Minni Singh

Biosensors for heavy metals

A biosensor is an analytical device that consists of an immobilized biocomponent in conjunction with a transducer, and represents a synergistic combination of biotechnology and microelectronics. This review summarizes the use of biosensors for detecting and quantifying heavy metal ions. Heavy metal contamination is of serious concern to human health since these substances are non-biodegradable and retained by the ecological system. Conventional analytical techniques for heavy metals (such as cold vapour atomic absorption spectrometry, and inductively coupled plasma mass spectrometry) are precise but suffer from the disadvantages of high cost, the need for trained personnel and the fact that they are mostly laboratory bound. Biosensors have the advantages of specificity, low cost, ease of use, portability and the ability to furnish continuous real time signals. The analysis of heavy metal ions can be carried out with biosensors by using both protein (enzyme, metal-binding protein and antibody)-based and whole-cell (natural and genetically engineered microorganism)-based approaches.

A Bacillus sphaericus Based Biosensor for Monitoring Nickel Ions in Industrial Effluents and Foods

A microbial-based biosensor has been developed based on enzyme inhibition bioassay for monitoring the presence of Ni(II) in real-time samples. The sensing element is immobilized Bacillus sphaericus MTCC 5100 yielding urease enzyme. The transducer is an NH 4 + ion selective electrode in conjunction with a potentiometer. Heavy metals are potentially toxic to human beings. Nickel is associated with causing adverse health effects such as dermatitis and vertigo, in humans. Toxicity is manifested by affecting T-cell system and suppressing the activity of natural killer cells. Nickel finds applications in electroplating, coinage, electrodes, jewellery, alloys. The foods rich in Ni(II) are nuts, beans, oats, and wheat. The range of Ni(II) detection by the developed biosensor is 0.03–0.68 nM (0.002–0.04 ppb) with a response time of 1.5 minutes. For application, the Ni(II) effluent was procured from an electroplating industrial unit and was found to have a concentration of 100.0 ppm Ni(II). In foods, wheat flour sample was acid digested and Ni(II) was specifically complexed in the presence of other cations, and had an Ni(II) concentration of 0.044 ppm. The developed system has a reliability of 91.5% and 90.6%, respectively, for the samples and could possibly replace the existing conventional techniques of analysis.

Biosynthesis of silver nanoparticles by natural precursor from clove and their antimicrobial activity

Silver nanoparticles (AgNPs) have attracted the attention of researchers because of their unique properties and applications in various fields, such as medicine, catalysis, textile engineering, and pollution treatment. The green synthesis of AgNPs has many advantages, such as less time requirement, highly stable AgNPs, better control over crystal growth, morphology, ease for scale up, and economic viability. Syzygium aromaticum (clove) was used for the extracellular biosynthesis of AgNPs. Eugenols are the active biomolecules present in clove, responsible for the bioreduction of AgNO3 (Ag+) leading to the formation and capping of AgNPs (Ag0). One molecule of eugenol releases two electrons and these two electrons will be taken by 2 Ag+ ions and these will get reduced to 2 Ag0. The synthesis of AgNPs was confirmed by the appearance of brown colour. The synthesized AgNPs were characterised by various techniques, such as UV-VIS spectroscopy, transmission electron microscopy, X-ray diffraction and Fourier transformed infrared spectroscopy. The synthesised AgNPs have λmax of 440 nm. It was evaluated that the AgNPs were biphasic in nature (cubic + hexagonal) with an average size of 50.0 nm. The synthesized AgNPs showed significant antimicrobial activity against Bacillus cereus NCDC 240 as they are nano-sized and have high surface area to volume ratio. AgNPs inhibit the growth of bacteria by various ways, such as by disrupting the cell membrane of bacteria, uncoupling the oxidative phosphorylation, inhibiting the DNA replication, forming free radicals and affecting the cellular signalling of bacteria leading to cell death.

L-arginine biosensors: A comprehensive review

Arginine has been considered as the most potent nutraceutics discovered ever, due to its powerful healing property, and its been known to scientists as the Miracle Molecule. Arginine detection in fermented food products is necessary because, high level of arginine in foods forms ethyl carbamate (EC) during the fermentation process. Therefore, L-arginine detection in fermented food products is very important as a control measure for quality of fermented foods, food supplements and beverages including wine. In clinical analysis arginine detection is important due to their enormous inherent versatility in various metabolic pathways, topmost in the synthesis of Nitric oxide (NO) and tumor growth. A number of methods are being used for arginine detection, but biosensors technique holds prime position due to rapid response, high sensitivity and high specificity. However, there are many problems still to be addressed, including selectivity, real time analysis and interference of urea presence in the sample. In the present review we aim to emphasize the significant role of arginine in human physiology and foods. A small attempt has been made to discuss the various techniques used for development of arginine biosensor and how these techniques affect their performance. The choice of transducers for arginine biosensor ranges from optical, pH sensing, ammonia gas sensing, ammonium ion-selective, conductometric and amperometric electrodes because ammonia is formed as a final product.

Arsenic Biosensors: Challenges and Opportunities for High-Throughput Detection

A detailed overview of arsenic biosensors and advancements is presented with particular emphasis on recombinant whole-cell-based biosensors employing engineered plasmid constructs with the inherent ars operon in cells as the basis of biorecognition. The review discusses the need for the development of rapid, sensitive, and accurate analysis of arsenic due to its widespread toxicity. New approaches for arsenic detection using nanosensor platforms as next generation biorecognition elements are detailed, suggesting their role in high-throughput detection. Though their use for arsenic biosensing is in its infancy and their precision in on-site detection is yet to be established, the capability of aptamer–graphene nanoensembles to augment conventional detection methods to be considered as reference points of action for risk assessments is proposed.

Chlorophyll based biosensor for sulfur mustard - a chemical warfare agent

Sulfur mustard (SM), a chemical warfare agent (CWA) is a bifunctional blistering and alkylating agent used in military warfare having antimitotic, mutagenic, carcinogenic, teratogenic and cytotoxic effects. Conventional techniques used for the detection of CWAs are complex, expensive and require sophisticated analytical procedures thus entailing the development of alternative analytical tools. Biosensors offer an alternative analytical approach with a promise of selectivity in addition to sensitivity, ease of use, rapid response and negligible sample pre-treatment. Furthermore, biomolecules have the ability to detect toxicity in addition to concentration. This work reports the development of a fluorescence based biosensor for detection of SM. 2-chloroethyl ethyl sulfide (2-CEES), a sulfur mustard mimic which is structurally similar to it but not as lethal was used for the study, utilizing the ability of chlorophyll to detect the said compound owing to fluorescence. For this, chlorophyll extract from a plant source was immobilized on fibre glass discs of 5mm diameter, and its fluorescence was studied by excitation at 437 nm and emission at 667 nm. The exposure of the biocomponent to 2-CEES led to quenching of fluorescence, which varied linearly with increasing concentration of 2-CEES with a detection limit of 7.68 × 10−10 M. The fluorescence drop mechanism was characterized by HPLC studies which confirmed the conversion of chlorophyll, upon exposure to the analyte, to non-fluorescing catabolic products. The low detection limit was a promising feature of the biosensor.