Xanthine biosensor based on XO/AuNP/PtNP/MWCNT hybrid nanocomposite modified GCPE

Advances in xanthine biosensors and sensors: A review

Xanthine is derived from hypoxanthine by xanthine oxidase (XOD), a flavoprotein containing molybdenum and non-haem iron, sulfur and from guanine by guanine deaminase enzyme. Xanthine is oxidized into uric acid by XOD. Xanthine is used as an indicator of fish freshness, based on the reactions in which ATP is degraded into xanthine and its quantity increases with time of fish death. Fresh fish meat is required in food industry for making high quality items. The determination of xanthine in biological fluids is also used in diagnosing and curing many diseases like renal failure, gout, xanthinuria, hyperuricemia. Various methods are available for detection of xanthine but most of them are complicated, time consuming less sensitive & specific and require expensive instrumental setup and trained person to operate. Enzyme based biosensors and non enzymic sensors overcome these disadvantages, as these are simple, rapid, specific, sensitive and easy to operate. Present review describes xanthine biosensors, which work optimally between pH 3.5-9.0, temperature 25 °C-65 °C, xanthine concentration ranging from 0.001-50 × 104 µM. These biosensors have also been used to measure xanthine concentration in beverages, urine and serum samples. Various modified electrodes have been discussed for the detection of xanthine using both enzymatic and non-enzymatic approaches in the present review.

Carbon Nanotube-Based Biosensors Using Fusion Technologies with Biologicals & Chemicals for Food Assessment

High-sensitivity sensors applied in various diagnostic systems are considered to be a promising technology in the era of the fourth industrial revolution. Biosensors that can quickly detect the presence and concentration of specific biomaterials are receiving research attention owing to the breakthroughs in detection technology. In particular, the latest technologies involving the miniaturization of biosensors using nanomaterials, such as nanowires, carbon nanotubes, and nanometals, have been widely studied. Nano-sized biosensors applied in food assessment and in in vivo measurements have the advantages of rapid diagnosis, high sensitivity and selectivity. Nanomaterial-based biosensors are inexpensive and can be applied to various fields. In the present society, where people are paying attention to health and wellness, high-technology food assessment is becoming essential as the consumer demand for healthy food increases. Thus, biosensor technology is required in the food and medical fields. Carbon nanotubes (CNTs) are widely studied for use in electrochemical biosensors. The sensitive electrical characteristics of CNTs allow them to act as electron transfer mediators in electrochemical biosensors. CNT-based biosensors require novel technologies for immobilizing CNTs on electrodes, such as silicon wafers, to use as biosensor templates. CNT-based electrochemical biosensors that serve as field-effect transistors (FET) increase sensitivity. In this review, we critically discuss the recent advances in CNT-based electrochemical biosensors applied with various receptors (antibodies, DNA fragments, and other nanomaterials) for food evaluation, including pathogens, food allergens, and other food-based substances.

An interference-free new xanthine biosensor based on immobilized enzyme-nanogold conjugate on carbon nanotube doped poly(3,4-Ethylenedioxythiophene) composite film

A new design of biosensor based on polymeric nano(bio)composite has been proposed for the selective detection of xanthine to be used in the clinical analysis as well as food quality control. The xanthine oxidoreductase (XOR) gene ofPseudomonas aerogenosastrain CEBP1 wascloned to obtainpurifiedenzyme through affinity chromatography. fMWCNTdoped PEDOTwas electrodeposited on the working electrodeto enhance the sensitivity and selectivity of the biosensor. Bio-synthesized gold nanoparticles conjugated XOR (Au-XOR) was covalently immobilized on the polymeric nanocomposite. The enzymatic activity was enhanced 1.12 times with increased substrate affinity. The surface morphology and structural properties of the polymeric layer were investigated using SEM, FESEM, TEM. Electrochemical characteristics were performed by cyclic voltammetry, differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy. Xanthine was oxidized (pH 7.0) on the uniquely designed polymeric nano(bio)composite modified electrode at a lower anodic potential of + 0.446 V vs. Ag/AgCl (3 M NaCl)at optimized DPV conditions. The simple, newly designed Au-XOR/fMWCNT-PEDOT/GCE exhibited interference-free reproducibility and stability (∼4 months) with excellent sensitivity of 16.075 µA.µM^-1.cm^-2for the quantification of xanthine in biological samples such as blood, tissue, urine. The applicability of thebiosensor was validatedby comparing the sensing results for the real biological fluidic solutions with HPLC data (RE = 0.5-3.1%).

Metal Nanoparticles for Electrochemical Sensing: Progress and Challenges in the Clinical Transition of Point-of-Care Testing

With the rise in public health awareness, research on point-of-care testing (POCT) has significantly advanced. Electrochemical biosensors (ECBs) are one of the most promising candidates for the future of POCT due to their quick and accurate response, ease of operation, and cost effectiveness. This review focuses on the use of metal nanoparticles (MNPs) for fabricating ECBs that has a potential to be used for POCT. The field has expanded remarkably from its initial enzymatic and immunosensor-based setups. This review provides a concise categorization of the ECBs to allow for a better understanding of the development process. The influence of structural aspects of MNPs in biocompatibility and effective sensor design has been explored. The advances in MNP-based ECBs for the detection of some of the most prominent cancer biomarkers (carcinoembryonic antigen (CEA), cancer antigen 125 (CA125), Herceptin-2 (HER2), etc.) and small biomolecules (glucose, dopamine, hydrogen peroxide, etc.) have been discussed in detail. Additionally, the novel coronavirus (2019-nCoV) ECBs have been briefly discussed. Beyond that, the limitations and challenges that ECBs face in clinical applications are examined and possible pathways for overcoming these limitations are discussed.

A Robust and User-Friendly Alternative to Densitometry Using Origami Biosensors and Digital Logic

Colorimetric detection with smartphones is ideal for point-of-care measurements because the signal reader is easily available. Densitometric detection schemes enable semiquantitative measurements but require a lightproof box to control photographic conditions and/or extensive data treatment to extract information. Approaches based on pattern recognition are not so sensitive to light artifacts but can only yield a yes/no type of answer when the signal is above or below a certain threshold. Here, we introduce a new method for detecting different concentrations of proteins as well as light artifacts with origami immunosensors and digital logic. The origami design consists of a folded piece of paper with three identical biorecognition sites so that one drop of sample generates three colorimetric signals simultaneously. The three colorimetric signals are then evaluated with an augmented reality app that generates a virtual semaphore that sequentially turns on its green, yellow, and red lights depending on the concentration of analyte. These three Boolean variables pass through "and" and "not" logic gates in a 3-to-8 decoder that enables the semiquantitative detection of proteins and adds a failsafe against erroneous results. The proposed method can detect the model analyte mouse IgG with a limit of detection and sensitivity comparable to densitometry performed under light-controlled conditions. It can also detect the sepsis biomarker procalcitonin at clinically relevant concentrations. With our approach, the detection is performed in real time, and signal processing is not required, which makes it suitable for rapid analyses by nonspecialists at the point of need.

Development of electrochemical biosensor for detection of pathogenic microorganism in Asian dust events

We developed a single-walled carbon nanotubes (SWCNTs)-based electrochemical biosensor for the detection of Bacillus subtilis, one of the microorganisms observed in Asian dust events, which causes respiratory diseases such as asthma and pneumonia. SWCNTs plays the role of a transducer in biological antigen/antibody reaction for the electrical signal while 1-pyrenebutanoic acid succinimidyl ester (1-PBSE) and ant-B. subtilis were performed as a chemical linker and an acceptor, respectively, for the adhesion of target microorganism in the developed biosensor. The detection range (10²-10¹⁰ CFU/mL) and the detection limit (10² CFU/mL) of the developed biosensor were identified while the response time was 10 min. The amount of target B. subtilis was the highest in the specificity test of the developed biosensor, compared with the other tested microorganisms (Staphylococcus aureus, Flavobacterium psychrolimnae, and Aquabacterium commune). In addition, target B. subtilis detected by the developed biosensor was observed by scanning electron microscope (SEM) analysis.