Category: News

Pillalamarri Srikrishnarka

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Key words: Wearable electronics, Flexible solar cells, TiO₂ nanotube

Chennai, India: Whenever we hear about wearable electronics, the most successful and widely accepted technology that reached the masses is in the form of a smartwatch. It is not only showing time, but it is also capable of counting steps, total distance moved, measuring heart rate, body temperature and even conducting ECG of human body.  This invention has completely transformed our way of life. The major limitation for such kind of wearable technologies is the power supply, the battery used is limited and needs charging for continued usage. This limits the overall usability of the system. Imagine if we have a smartwatch that doesn’t need any charging!

In this context, extensive research has been conducting and researchers from Fudan University and EMPA were successful in fabricating solar concentrators for fiber solar cells.

So, before directly going to the fabrication procedure and the detail technology inside it, let’s first look into the basics of what is a solar cell and solar concentrator means. A solar cell is a device that converts light energy into electricity and a solar concentrator helps further in improving the solar cell’s efficiency. Sun is our abundant source of energy and thus we need to effectively and efficiently use that energy for powering our daily use electronic gadgets. Solar panels are one of the prime examples for efficient power production, however, the cost of the panels and carry such kind panels during mobility restrict their uses in such purpose.  Since, it lacks flexibility, solar panels, can’t be worn on clothes and is limits its further uses. Let’s limit the focus of this article towards mobility alone. In the past, a series of reports which have been addressed for this purpose and researchers have come up with flexible solar cells in this context. The seminal work by Prof. Graetzel of EPFL, Switzerland, who invented the dye-sensitized solar cell totally revolutionized the field of photovoltaics. A dye-sensitized solar cell consists of a photoanode which is made of semiconducting metal oxides typically of tin, zinc and titania. This photoanode is then bleached in a dye, which could be of natural or synthetic origin, is then immersed in an electrolyte solution and finally platinum or carbon is used as the photocathode.

In the current article written by Huang et al., authors initially fabricated a flexible fiber-based dye-sensitized solar cell. [1] Consisting of a titanium wire which was anodized to form flexible titanium dioxide nanotubes (TN). Further, carbon nanotube (CN) fiber was initially fabricated by a technique known as floating catalyst chemical vapor deposition. As a result of this process, the obtained CN fibers intertwined with the TN fibers were achieved and this structure was used as photoanode of the device. This composite fiber-wire is then immersed in N719 dye and the electrolyte and cell has been fabricated by making a sandwich structure with the photoanode and photocathode. Finally, a methacryloxypropyl- terminated polydimethylsiloxane with a UV-initiator along with a fluorescent dye known Comarin 6 was used as a solar concentrator. Multiple flexible solar cells were taken and the above solution was poured on these fibers and a film was made. Upon drying, the film was tested under a solar simulator and the researcher observed an enhancement of 84 % in the conversion efficiency and taking the device efficiency to ~7.89 %. With multiple flexible solar cell fibers with a 3 cm² area of the solar concentrator, they have obtained a power output of 0.89 mW, which is substantial to energize the smart watch.

References:
[1] Chieh-Szu Huang et al. J. Mater. Chem. A, 2021, DOI: https://doi.org/10.1039/D1TA04984D  (Just accepted)

Pillalamarri Srikrishnarka

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Key words: Chlorofluorocarbons (CFC), Montreal treaty, Global warming, Greenhouse

Chennai, India: Before directly going into the Montreal protocol, let’s travel back in time where we have read that the earth’s surface is protected from the harmful UV radiations coming from the sun. It’s a thin layer of ozone (O3) that is formed when a nascent oxygen species react with oxygen forming a particularly dense molecule that is highly efficient in absorbing the UV radiations. Typically present at 25 km from the earth’s surface and protecting us from skin cancer. Thinning of this protective layer was observed by Farman, Gardiner and Shanklin in 1985 over the Halley and Faraday stations in Antarctica [1]. There was about ~16 % decrease in the overall density of the O3 layer and it has been raised a serious concern. Upon further investigation into what led to this decrease, they understood the chlorofluorocarbons (CFCs) are the main culprits. These CFCs were commonly present in propellants, as coolants in refrigerators and also for aerosolizing paint and scent. The global body met in 1987 in Montreal and signed a treaty to phase out the manufacture and sale of CFC-based gadgets by 2010. This has been a success story, where a collective work led to an overall decrease in the CFC consumption and there has been a significant O3-hole coverage. However, due to the high lifetime (~ 50 years) of the CFCs, the atmosphere can fully recover only by 2050.

Now, let us consider a scenario wherein if there was no Montreal treaty and we continued the rampant usage of CFCs coupled with the increased consumption of fossil fuels, which caused an increase in the overall concentration of greenhouse gases in the atmosphere. Recently, a paper was published where the scientists have simulated a scenario that deals with the above question, the outcome is rather warming (pun aside). In their simulation, they have considered 3 scenarios; the first one, where the simulation follows the present time(with no control over the production of CO₂ and the other greenhouse gases, but there is a ban on CFCs), the second one where the ozone layer was fixed in 1960 but no control over the production of CO₂, and other greenhouse gases and the third is where there was no Montreal treaty and there is rampant usage of CFCs. The simulation was based on past historical data and predictions till 2100. Let’s look into their extreme scenario where there was no control over the production and consumption of the CFCs.

In figure 1a, we see the depletion in the ozone layer from the year of 2000 in both scenarios 1 and 3.However, there was a significant decrease after 2040 in the case of third scenario, where there was no Montreal treaty. Overall ~70 % decrease in the ozone layer was projected at the end of this century.

They observed an increase in the production of greenhouse gases till 2075, however, thisrise was decelerated in all of their simulations. What does this lead to? There was a steady rise in the temperature of the earth due to global warming. With the absence of the ozone layer by the end of the century, they observed an increased temperature by 6 k compared to that of 3.3 k. This increased temperature surely impacts everyone on the planet. Plants are the major source for carbon fixation, i.e., they inhale CO₂, convert them into energy and release O₂ into the atmosphere. What happens to this conversion when there is abundant UV radiation in the absence of the protective ozone layer? For every 10% increase in UV radiation, they observed a 3% reduction in the fixation. We might feel 3% is so minuscule and should it matter? Because of the poor carbon fixation, by the end of the century, the CO₂ concentration doubled from 400 ppm to ~900 ppm. This news not only predicts the grim future if we don’t take care of our environment, but also the importance of the Montreal treaty which will save our planet.

The Montreal treaty is a success story, we need to remind ourselves that we all must towards the collective good over individual greed and make this world a better place for the future generation. All the governing bodies must meet regularly and implement the Paris Accords at the individual level, so that we can reduce global warming to less than 1.5 ^oC.

Source:
[1] PaulJ.Young et al.Nature,2021, 596, 384–388.
https://www.nature.com/articles/s41586-021-03737-3

Pillalamarri Srikrishnarka

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Key words: SARS-CoV-2, RT-PCR, COVID, Biosensor, Liquid-gated FET

Chennai, India: Presently, the world is dealing with the outbreak of a respiratory illness caused by the severe acute respiratory syndrome coronavirus – 2 also known as (SARS-CoV-2). Being a successor to SARS-CoV-1 which was responsible for the 2002-2004 SARS outbreak, is highly contagious as the transmission primarily occurs via aerosols. [1] The virion typically ranges between 50-200 nm in diameter having four structural proteins known as the spike, envelope, membrane and nucleocapsid. [2] Testing-tracking and treating is the current strategy followed globally for controlling the pandemic. Nucleic acid testing using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) is the golden standard for diagnosing COVID-19. However, this methodology requires sample purification, amplification and trained professionals which reduces the overall efficiency of the testing system.

To mitigate some of these limitations, there have been strides made using colloidal gold particles-based lateral flow assay, enzyme-linked immunosorbent assay and luminescence-based biosensors. However, for most of these sensors, the detection limit reaches a maximum of 2.8 fM. (where 1fM is 10^-15 M). This limitation could become a factor while managing COVID when the antibody concentration is below this value. Therefore, while studying the vaccine efficacy, a sensor that can detect even the smallest concentration of antibodies is needed. In this regard, Hang et al., from Fudan University recently developed a graphene-based field-effect transistor for detecting SARS-CoV2 antibodies. Monolayered graphene films were initially prepared using chemical vapor deposition on copper foils. Graphene from these copper foils was then transferred onto SiO2/Si substrate using the wetting method. In this method, graphene is first transferred to phenyl methyl ether solution containing polymethyl methacrylate. Graphene was later transferred onto a SiO2/Si substrate from PMMA. The graphene is then functionalized with 1-pyrenebutyric acid N-hydroxysuccinimide ester (PASE) molecules through the pi-pi coupling. The spike S1 protein of SARS-CoV2 is then anchored to PACE via the amine group present on the protein with the hydroxyl-free succinimide esters present on PASE. Finally, an open well was created on the SiO2/Si substrate using PDMS, this helps in holding the sample solution.

This sensor comprises a liquid-gated FET with Ag/AgCl reference electrode which is inserted in the electrolyte as gate electrodes. The electrolyte/graphene interface serves as a dielectric layer when a liquid-gate bias is applied externally. Current response to external voltage was measured. At a particular voltage, a drop in current was observed. As soon as the antibody was dropped on the sensor within 15 min there was a shift in the voltage. A calibration curve was obtained by varying the concentration of antibodies and the voltage shifts were noted. Using this sensor, a concentration of 2.6 aM was achieved. How is this possible? Is a simple question that everyone gets, graphene is wonder material having an atomic layer thickness due to this the surface is covered completely with the receptor which helps in higher sensitivity. The detection result is read out directly from the electric response without needing any complex further processing and data analysis. Such chips can be manufactured large-scale at a relatively low cost. It does hold a great promise for on-site point-of-care detection of SARS-CoV-2 thus mitigating cross-infection and accessibility for testing at home. These results have been published in the journal NANO Letters. [3]

Sources:
[1] https://www.nature.com/articles/d41586-020-02058-1
[2]Philip V’kovski et al. Nat Rev Microbiol.  2020, 1–16.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7592455/
[3] Hua Kang et al. Nano Lett.2021, 21, 19, 7897–7904.
https://doi.org/10.1021/acs.nanolett.1c00837

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Correspondence prepared by: Sourabh Pal, Indian Institute of Technology, Kharagpur, India, email: sourabhelt92@gmail.com (18:01:2021 and 14:00)

Key Words: supercapacitor, graphene, nanogenerator, nanosheets

India: An emerging new field of research that combines the strengths and capabilities of electronics and textiles into one is wearable electronics, opening new opportunities for electronic industry. It is also known as smart fabrics, which not only constitute wearable capabilities like any other garment, but also have local  monitoring, computation and as well as wireless communication potentials. Technology is indeed the main catalyst that can swiftly transform health care and the practice of medicine. So, any technology which can minimize the loss of human life and enhance the quality of life has undoubtedly a priceless value. In this aspect, the wearable electronics fulfills the dual roles of being a flexible information infrastructure that will facilitate the prototype of universal computing and a system for monitoring the vital signs of individuals in an efficient and cost-effective manner with a widespread interface of clothing. Wearable technology has already been offering versatile applications for consumers, emergency services and military users. Currently, the wearable technology companies and developers are now looking for novel ideas and conceptions to come up with advanced wearable devices that can serve the needful to the consumers.

However, the traditional wearable electronic devices require external power sources for powering. In this context, the main shortcoming lies in the low power density and limited stretchability of the external power sources. Hence, as a savior, micro-supercapacitors are the ideal energy storage devices that can be an excellent replacement of conventional batteries in wearable platform. Typical micro-supercapacitors usually demonstrates a sandwich-like stacked geometry that exhibits poor flexibility, long ion diffusion distances and a complex integration process when combined with wearable electronics. To overcome this ambiguity, in 2020, a research team of Penn State, Minjiang University and Nanjing University has explored an alternative device configuration and integration techniques to provide an advancement of micro-supercapacitors in wearable electronic applications [1]. Prof. Cheng and his team have utilized 3D laser-induced graphene foam and non-layered, ultrathin zinc-phosphorus nanosheets to construct the island-bridge type design of the micro-supercapacitor cells, leading to drastic improvements in electric conductivity and the number of absorbed charged ions. This offers the essential confirmation that these unique micro-supercapacitor arrays can charge and discharge efficiently and can store the energy needed to power a wearable device simultaneously. The researchers have also successfully integrated this system with a triboelectric nanogenerator, an emerging energy harvester that converts external mechanical energy to electrical one. Hence, this wireless charging element which can efficiently harvest energy from everyday human motion, unquestionably paves a new horizon towards high-performance stretchable and wearable electronic systems..

Sources:
[1] C. Zhnag et. al. Nano Energy, 81, 105609 (2021).
https://www.sciencedirect.com/science/article/pii/S2211285520311824

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Key Words: SERS, Gallbladder, Gold Nanostructure, Nickel foam

Human body is believed to be a well developed machine that can perform complex operations. Gallbladder is a very important part of human organ system. It accumulates particular fluid called ‘bile’ which can break down the fat present in the consumed food and thus helps digestion process. However, any problem in the Gallbladder system can create several health problems such as severe abdominal pain, jaundice, gallstones. In extreme cases when the growth of stones is dominant, patients are left with the option of surgery to get rid of the stones or the removal of entire gallbladder in worst condition. Thus proper diagnosis of Gallbladder related diseases is very much essential to lead a healthy life.

Most of the disease diagnosis methods are based on spectroscopy i.e. the interaction between matter and electromagnetic radiation. In this context, Surface-enhanced Raman scattering (SERS) is believed to be a potential spectroscopic tool, named after the pioneering Indian scientist Sir. C. V. Raman. Recently, Prof. H. Chung and co-workers have reported an advanced SERS-based technique capable of direct measurement of raw bile juice to identify any Gallbladder related disease in the upcoming issue of the journal Sensors & Actuators, B:  Chemical [1]. Over other known techniques the reported method is believed to be advantageous as it doesn’t require any pre-treatment process and thus becomes a handy analytical route for fast screening. The group has developed a paper strip based system where specially designed gold nanostructure (of dendrite shape) has been encaged over nickel foam (a cage like morphology of nickel). In this study, Gold nanostructure has been chosen owing to its high SERS efficiency. With such experimental designing, the team has studied the discrimination of various samples of raw bile juice collected from Gallbladder stone and Gallbladder polyp patients. According to the authors, although the reported method is very promising, future activities on accuracy, sampling range etc. are to be performed for making the technique applicable for clinical analysis.

Sources:
[1] T. D. Vu et. al. Sens. Actuators B Chem., 329,129238 (2021).
https://www.sciencedirect.com/science/article/abs/pii/S0925400520315781

The 2020 Meet with Science and Technology in Portugal (encontro CIÊNCIA’20) is now on progress (3^rd and 4^th of November). Current edition of the annual meeting of Portuguese researchers aims to promote a wide debate on the main topics and challenges of the scientific agenda beyond the world of scientific investigation. The main objective is to encourage not only the participation from diverse fields/sectors, but also to create and enhance the interaction among researchers, the business sector and the general public. Hence, there lies the main attraction of this event to various levels of society as this is a platform to connect science and technology together with the general public in a very popular way. Also, Nobel laureates take part to expand their experiences to the common people.

This Science Meet is promoted by the Foundation for Science and Technology (FCT) in collaboration with Ciência Viva – National Agency for Scientific and Technological Culture and the Parliamentary Education and Science Commission, and has the institutional support of the Government through the Minister of Science , Technology and Higher Education. “The main motto of the Science 2020 Meeting will be the importance and challenges of science, research and innovation in the recovery of Portugal in times of pandemic, making this country and Europe more resilient, more digital, greener, more social and more global” [1].

Many scientific and technological demonstrations are going on in which several eminent groups from research and industry fields are participating. Among many others, the group of Elvira Fortunato and Rodrigo Martins from ‘Institute of Nanostructures, Nanomodeling and Nanofabrication, Faculty of Science and Technology, Universidade Nova de Lisboa’ (CENIMAT-i3N) is no doubt a very famous and well-recognised one in their field (Materials Science) from Portugal. They have presented their contribution on ´´Systems for converting mechanical to electrical energy for autonomous low-consumption devices´´ [2]. In this demonstration, several prototypes which are developed at CENIMAT-i3N (FCT UNL) during different international and national research projects are presented, to show the conversion of the mechanical energy of movements to electrical energy. This kind of energy harvesters are now an emerging field of research and application as they reuse the wasted energy in daily body movements/dynamical motions by converting them into the electrical energy that can be further utilized to power up several portable devices and applications. To demonstrate in a simple way to the general public, the development processes of these devices with planar or linear configurations are also exhibited, as well as their application when connecting simple electrical devices such as an analog clock and LEDs. In the video link [2], it is quite interesting to find the details about how different kind of biocompatible polymers and substrates like carbon and textile fibers have been coated with several energy harvesting materials (piezoelectric or tribo-electric or mechano-electrical) and then designed to develop the device prototypes [3-6]. This new kind of mechanical energy harvesters can have immense impact in reaching the sustainable development goals, as well to extend a new stream for renewable energy applications for a better, greener and cleaner environment.

References:
[1] https://www.encontrociencia.pt/index.php
[2] https://www.youtube.com/watch?v=cIiRqn7rqZs
[3] G. Ferreira, S. Goswami, S. Nandy, L. Pereira, R. Martins, E. Fortunato, Advanced Functional Materials 2020, 30, 1908994
[4] S. Goswami, A. dos Santos, S. Nandy, R. Igreja, P. Barquinha, R. Martins, E. Fortunato, Nano Energy 2019, 60, 794
[5] A. Rovisco, A. dos Santos, T. Cramer, J. Martins, R. Branquinho, H. Águas, B. Fraboni, E. Fortunato, R. Martins, R. Igreja, P. Barquinha, ACS Applied Materials & Interfaces 2020, 12, 18421-18430
[6] A. dos Santos, N. Pinela, P. Alves, R. Santos, E. Fortunato, R. Martins, H. Águas, R. Igreja, Advanced Electronic Materials 2018, 4, 1800182.

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Correspondence prepared by: Debdatta Panigrahi, National Institute for Materials Science, Japan, email: debdattapanigrahi123@gmail.com (21:10:2020, 10:30)

Key Words: Logic Gate, Transistor, Antiambipolar, Inverter   

Tokyo: An inverter is a logic gate (termed as “NOT” gate) that is used to invert the applied input signal. Conventional binary inverters can handle two logic states, “1” and “0”. If the applied input is low (“0”) the inverter output becomes high (“1”) and vice versa. Since the early days of digital electronics, binary inverters have been one of the key components of integrated circuits and become the basic building blocks of every sophisticated electronic device that we use in our daily lives today-smartphones, laptops, tablets and many others.

Of late, we are witnessing another significant technological revolution that could possibly have even more positive impact on modern information technology, the emergence of organic semiconductor based ternary inverters which can exhibit three distinct logic states; “1”, ‘1/2” and “0”. With the approaching end of Moore’s Law (which states that the number of transistors on a microchip doubles every two years), the logic data density in binary integrated circuits can hardly be further improved due to the physical limitation. In this aspect, ternary logic can be a promising substitute to the binary logic owing to their capacity of handling higher density of information and their compatibility with low-power, high speed and less complex digital logic design technology. Ternary logic systems can drastically reduce the number of connections between devices inside the chip by transmitting more information, thereby simplifying the integrated circuit design and implementation [1].

Recently, a new genre of pn-junction transistors (termed as “antiambipolar transistors”) have been exploited for the realization of ternary inverters owing to their negative differential resistance characteristics. So far, several materials have been employed for the implementation of high performance antiambipolar transistors and low voltage operable, well balanced ternary inverters [2-4]. In particular, ternary logic circuits fabricated with organic semiconductors have several advantages compared to their inorganic counterparts [5-6]. First of all, organic semiconductors provide the advantages of easy and low-cost deposition and patterning processes. Another important advantage of this class of semiconductors is their intrinsic mechanical flexibility, which offers the scope of flexible and wearable electronics. They are capable of withstanding mechanical stresses, giving compatibility with the flexible substrates. Therefore, simultaneous attainment of mechanical flexibility and high data processability is possible in organic ternary inverters. Moreover, the strong optical absorption of the organic semiconductors enables the fine-tuning of their electronic properties, which can open up the possibility of new optoelectronic interconnection devices for next generation information technology.

Sources:

[1] S. L. Hurst, IEEE T. Comput. 12, 1160 (1984).
https://www.computer.org/csdl/journal/tc/1984/12/01676392/13rRUIIVljg

[2] Y. Wakayama, R. Hayakawa, Adv. Funct. Mater. 30, 1903724 (2019).
https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201903724

[3] M.Huang et. al. Nat. Nanotechnol. 12, 1148 (2017).
https://www.nature.com/articles/nnano.2017.208

[4] J. Shim et. al. ACS Nano 11, 6319, (2017).
https://pubs.acs.org/doi/abs/10.1021/acsnano.7b02635

[5] K. Kobashi et. al. Nano lett. 18, 43559 (2018).
https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.8b01357

[6] H.Yoo et. al. J. Adv. Mat. 31, 1808265 (2019). https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201808265

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Correspondence prepared by: Sayan Bayan¹ and Suman Chakraborty², ¹S. N. Bose National Centre for Basic Sciences, Kolkata, India, email: sayan.bayan@gmail.com, ²Physical Research Laboratory, Gujrat, India, email: suman.chakrabarty37@gmail.com (16:10:2020 and 14:00)

Key Words: Black holes, Event horizon, General Theory of Relativity, Singularity

India: The Nobel Prize in Physics for the year 2020has been awarded in one half to Roger Penrose“for the discovery that black hole formation is a robust prediction of the general theory of relativity” and the other half jointly to Reinhard Genzel and Andrea Ghez “for the discovery of a supermassive compact object at the centre of our galaxy”. Henceforth, the three scientists shared this prize for their outstanding discoveries about the ‘black hole’ which is considered as one of the most mysterious themes in Physics. To give a thought on their discovery, one needs to understand what are black holes and why are they so mysterious?

A black hole can be defined as a region in space where gravity is so strong that even light cannot escape through it. The black hole is enclosed by a boundary called ‘event horizon’ which defines the region where the velocity required to escape exceeds the speed of light [1]. Such strong gravity originates from the fact that matter gets squeezed into a very tiny space. Such a situation can be realized during the death of a star having mass more than three times the mass of the Sun. Since light cannot get out of black holes, it is conventionally invisible in naked eyes. However, a black hole can be realized by the virtue of its gravitational pull on other stars around it. The strong gravitational force of a black hole will pull matter from other stars. During this process, the compression and heat generation (in millions of degrees) will lead to the production of X-rays that radiate in space. Thus the outward region of the black hole can be realized by the emission of X-rays. In many occasions, the spreading of radio waves has also been witnessed [2].

Now back to the past, theoretically, the existence of black holes has been traced from Einstein’s general theory of relativity, although Einstein himself denied the concept of black holes. According to this theory, the force of gravity arises from the warping of spacetime (fusion of three dimensional space and one dimensional time) around a body. The core of this theory is some nonlinear equations known as Einstein field equations. Soon after the appearance of this theory, Karl Schwarzschild found the non-trivial solution of the Einstein field equations which led to the concept of gravitational collapse and the condition of singularity [3]. A singularity is a location where the gravitational field becomes infinite. However, the concept of singularity was debated a lot as many scientists attempted to prove that singularities don’t appear in generic solutions. In 1955, A. K. Raychadhuri’s work remarkably transformed the field of general theory of relativity as the equations laid by him formed the basis of all singularity theorems [3]. The defining moment came with the singularity theorem in 1965 where Penrose sparked the idea of incompleteness to describe singular spacetime and for the first time he introduced the concept of a closed trapped surface. The concept of a closed trapped surface reveals the inner region of an event horizon and can be assumed as the surface from which light is not moving away. Thus Penrose established that singularities appear generically and concluded with his Nobel winning discovery. Penrose’s singularity theorem was ample and straightaway and led to the development of modern singularity theorems [3].      

Penrose established the existence of black holes theoretically, while teams led by Ghez and Genzel’s demonstrated experimental evidence of such celestial giants at the heart of our Galaxy. Since a long time physicists suspected that most galaxies include a supermassive black hole at the centre. The bright Sagittarius A* (Sgr A*) – a radio source situated at the centre of Milky Way, was suspected as a black hole. In the 1980s, Genzel and Charles Townes (another Nobel laureate) exploited InfraRed (IR) spectroscopy to track gas clouds orbiting at the centre of the Milky Way. Although they could infer the presence of a massive, compact source of gravitation, the evidence was not ultimate.

The prime challenge was to detect the emission from the stars amidst the gas and dust obstacles. However in 1990, teams led by Ghez and Genzel came out to address this issue with the world’s biggest telescopes which work in the near-IR region suitable for sensing the light that can escape the dusty region of the galactic centre.  Ghez and her team used the Keck Observatory, Hawaii, while Genzel and his co-workers used the Very Large Telescope on Cerro Paranal, Chile. With a series of developments in imaging techniques, they could improve the resolution and sensitivity to the faint light from the celestial world.

The two teams tracked and plotted the tracks of several stars near the centre of the galaxy for a decade, particularly the star called S0-2 by Ghez’s group or S2 by Genzel’s team.  This led to the understanding that the motion and pattern of the stars are influenced by the presence of an invisible source of four million solar masses and which is certainly a supermassive black hole [4]. This was not only the strongest evidence of the presence of the giant black hole at the galaxy’s core, but also stimulates research on the immense gravitational effects on its stellar neighbours.

Sources:
[1] https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
[2] https://science.nasa.gov/astrophysics/focus-areas/black-holes
[3] J. M. M. Senovilla, D. Garfinkle, Class. Quantum Grav., 32, 124008 (2015).
https://iopscience.iop.org/article/10.1088/0264-9381/32/12/124008
[4] www.timesonline.co.uk/tol/news/uk/science/article5316001.ece

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Correspondence prepared by: Dr. Md Palashuddin Sk, Assistant Professor of Aligarh Muslim University, Uttar Pradesh, India, email: palashuddin.ch@amu.ac.in (12:10:2020, 17:30)

Key Words: Haemoglobin, Carbogenic Dots, luminescence, nanocrystals

Aligarh: Haemoglobin (Hb) is an essential iron-containing protein, which exists in the red blood corpuscles. Hb consists of four iron-porphyrin units (heme) together with the globular protein moiety. Atomic iron encaged into the heme moiety plays a crucial role in transporting molecular oxygen (O₂) from the respiratory organs to the different parts of our body through blood and carrying the major portion of carbon dioxide from these parts to the lungs at the same time. The Hb level in blood to the well-functioning of the organism in the human body is 13.0-18.0 g/dL and 12.0- 16.0 g/dL for male and female, respectively [1]. On the contrary, Hb amount below this level solely causes several blood disorder diseases (even fatality) such as thalassemia, anaemia, and leukaemia. Approximately, two billion people (mainly women and children), worldwide suffer from particular anaemia due to the lower level of Hb in blood. The lower level of Hb thus becomes a major issue and hence is of substantial significance for clinical diagnosis purposes. In this regard, the sensitive detection and determination of Hb in clinical diagnostics is essential to assess the extent of blood disorder diseases and to evaluate various intervention programs aimed at control of the same.

There are quite a few analytical methods like electrochemical, colorimetric, and various spectroscopic techniques are generally employed for the detection of Hb in the blood. Unfortunately, most of these techniques require harsh, expensive chemicals, tedious and complicated probe preparation and of low sensitivity detection ability as well.  In this scenario, the luminescent carbogenic dots (Cdots) are paid great attention due to their higher water solubility, biocompatibility, high quantum yield, and excellent optical (stability towards the chemical/physical environment changes such as pH, ionic strength, etc.) and well enough chemical stability.

Following this trend, our Research Group at Aligarh Muslim University, India, has recently developed a Hb sensor from the reaction by-product, which is accidentally isolated during the synthesis of tin oxide (SnO₂) nanocrystals [1]. The purified by-product is confirmed as luminescent carbogenic dots which is again produced due to the polymerization and consequent carbonization of the excess of 4,7,10-trioxa-1,13-tridecanediamine (TTDDA). Yet, TTDDA is a hazardous reagent, it is used as a stabilizing agent in metal nanocrystals synthesis [1]. The advantage of such synthesis lies in the fact that the obtained product SnO₂ nanocrystals and the reaction side product are environmentally friendly and are produced through the sustainable way. Our Research Group has actually employed the principle of luminescence turn-off property of Cdots with the interaction of Hb to develop a diagnostic method for qualitative and quantitative detection of Hb in the blood. The observed luminescence property of the Cdots remains highly selective towards the detection of a trace amount of Hb. Efficient ground state complexation between Cdots and Hb is solely responsible for the unprecedented selectivity of Cdots towards Hb detection. Keeping in mind the issues of accuracy in the visual detection, economic factors and the portability, we have further developed a fluorescent test strip-based sensing method. The rapid sensing experiment by using the fluorescent test strip has also been studied with the voluntary collection of blood samples, and various interfering chemical substances, proteins, amino acids, metal ions, anions, etc at pH ~7.4 in order to realize the selectivity as well. Upon addition of Hb, the emission intensity of Cdots is drastically reduced; while, in the case of other analytes addition, hardly any reasonable change in the intensity observed, validating the accuracy of the test strip. Test strip-based luminescence turn-off property of Cdots in the presence of Hb further defines their applicability in fabricating portable and inexpensive sensing devices. Even the trace amount of blood present in the human urine is also possible to be detected by this paper-based method, the author stated. The present paper strips based detection technique has advantages over conventional methods (absorption-based spectroscopic methods) because of the portability, cost-effectiveness, time-saving, high sensitivity, ease to measuring Hb, requiring minimum instrumentation and so forth. The user-friendly nature of this technique is quite desirable and beneficial mainly in the remote areas or primary health care centres to monitor the Hb level of patients.

Sources:
[1] F. Arshad et. al., New J. Chem., 44, 6213 (2020)
https://pubs.rsc.org/en/content/articlelanding/2020/nj/d0nj00401d#!divAbstract