Manil Kukkar

A label-free electrochemical immunosensor for the detection of cardiac marker using graphene quantum dots (GQDs)

A label-free immunosensor based on electrochemical impedance spectroscopy has been developed for the sensitive detection of a cardiac biomarker myoglobin (cMyo). Hydrothermally synthesized graphene quantum dots (GQDs) have been used as an immobilized template on screen printed electrodes for the construction of an impedimetric sensor platform. The GQDs-modified electrode was conjugated with highly specific anti-myoglobin antibodies to develop the desired immunosensor. The values of charge transfer resistance (Rct) were monitored as a function of varying antigen concentration. The Rct value of the immunosensor showed a linear increase (from 0.20 to 0.31kΩ) in the range of 0.01-100ng/mL cMyo. The specific detection of cMyo was also made in the presence of other competing proteins. The limit of detection for the proposed immunosensor was estimated as 0.01ng/mL which is comparable to the standard ELISA techniques.

One step in-situ synthesis of amine functionalized graphene for immunosensing of cardiac marker cTnI

2-Aminobenzyl amine (2-ABA) functionalized graphene is proposed for the ultrasensitive immunosensing of Cardiac Troponin I (cTnI). 2-ABA was electrochemically polymerized on the graphene decorated interdigitated electrode to obtain the amine functionalized graphene (f-GN). The f-GN electrode was then modified with monoclonal anti-cTnI antibodies via Schiff reaction based chemistry. Detailed characteristics of the processes involved and the finally developed antibody conjugated f-GN interdigitated electrode have been studied. The above micro-device was used in a drain source configuration for the sensing of cTnI. A wide dynamic linear range of antigen detection (0.01-1ng/mL) is achieved with the limit of detection of 0.01ng/mL. The utility of the proposed sensing technique is demonstrated by successfully testing the antigen concentration in spiked serum samples.

Rapid extraction and quantitative detection of the herbicide diuron in surface water by a hapten-functionalized carbon nanotubes based electrochemical analyzer

A solid phase extraction micro-cartridge containing a non-polar polystyrene absorbent matrix was coupled with an electrochemical immunoassay analyzer (EIA) and used for the ultra-sensitive detection of the phenyl urea herbicide diuron in real samples. The EIA was fabricated by using carboxylated carbon nanotubes (CNTs) functionalized with a hapten molecule (an amine functionalized diuron derivative). Screen printed electrodes (SPE) were modified with these haptenized CNTs and specific in-house generated anti diuron antibodies were used for bio-interface development. The immunodetection was realized in a competitive electrochemical immunoassay format using alkaline phosphatase labeled secondary anti-IgG antibody. The addition of 1-naphthyl phosphate substrate resulted in the production of an electrochemically active product, 1-naphthol, which was monitored by using differential pulse voltammetry (DPV). The assay exhibited excellent sensitivity and specificity having a dynamic response range of 0.01 pg mL(-1) to 10 μg mL(-1) for diuron with a limit of detection of around 0.1 pg mL(-1) (n = 3) in standard water samples. The micro-cartridge coupled hapten-CNTs modified SPE provided an effective and efficient electrochemical immunoassay for the real-time monitoring of pesticides samples with a very high degree of sensitivity.

A New Electrolytic Synthesis Method for Few-Layered MoS2 Nanosheets and Their Robust Biointerfacing with Reduced Antibodies

We report an efficient method for the synthesis of few-layered MoS2 nanosheets and demonstrate their application in the label-free detection of the prostate-specific antigen (PSA) cancer marker. As a novel strategy, the electro-dissolution of molybdenum metal sheets in the presence of Na(+) and S(2-) ions led to the formation of Na(+) intercalated MoS2. Further exfoliation by ultrasonication yielded the desired formation of few-layered MoS2 nanosheets. After comprehensive characterization, the synthesized MoS2 nanosheets were channeled in a field-effect transistor (FET) microdevice. Chemically reduced anti-PSA antibodies were immobilized on the MoS2 channel above the FET microdevice to construct a specific PSA immunosensor. The antibodies were deliberately reduced to expose the hinge-region disulfide bonds. This approach offered a robust and site-directed immunosensing device through biointerfacing of the sulfhydryl groups (-SH) in the reduced antibody with the surface S atoms of MoS2. This device was validated as an effective immunosensor with a low detection limit (10(-5) ng/mL) over a wide linear detection range (10(-5) to 75 ng/mL).

Formation of High-Purity Indium Oxide Nanoparticles and Their Application to Sensitive Detection of Ammonia

High-purity In2O3 nanoparticles were recovered from scrap indium tin oxide substrates in a stepwise process involving acidic leaching, liquid-liquid extraction with a phosphine oxide extractant, and combustion of the organic phase. The morphological and structural parameters of the recovered nanoparticles were investigated to support the formation of the desired products. These In2O3 nanoparticles were used for sensitive sensing of ammonia gas using a four-probe electrode device. The proposed sensor offered very quick response time (around 10 s) and highly sensitive detection of ammonia (at a detection limit of 1 ppm).

Synthesis of Poly(ϵ-caprolactone) Microreactors from Freeze-Dried Microspheres

Poly(ϵ-caprolactone) microreactors were prepared by micro-volcanic rupture of freeze dried microspheres. Effects of three synthesis parameters viz polymer concentration, emulsifier concentration and stirring speed on size and morphology of microreactors were examined. Average diameter of microreactors showed substantial increase with increasing polymer concentration and reduced size with increasing polyvinyl alcohol (emulsifier) concentration and stirring speed, respectively. These miniaturised structures have potential applications in immunodiagnosis and drug delivery.

A comprehensive review on nano-molybdenum disulfide/DNA interfaces as emerging biosensing platforms

The development of nucleic acid-based portable platforms for the real-time analysis of diseases has attracted considerable scientific and commercial interest. Recently, 2D layered molybdenum sulfide (2D MoS2 from here on) nanosheets have shown great potential for the development of next-generation platforms for efficient signal transduction. Through combination with DNA as a biorecognition medium, MoS2 nanostructures have opened new opportunities to design and construct highly sensitive, specific, and commercially viable sensing devices. The use of specific short ssDNA sequences like aptamers has been proven to bind well with the unique transduction properties of 2D MoS2 nanosheets to realize aptasensing devices. Such sensors can be operated on the principles of fluorescence, electro-cheumuluminescence, and electrochemistry with many advantageous features (e.g., robust biointerfacing through various conjugation chemistries, facile sensor assembly, high stability with regard to temperature/pH, and high affinity to target). This review encompasses the state of the art information on various design tactics and working principles of MoS2/DNA sensor technology which is emerging as one of the most sought-after and valuable fields with the advent of nucleic acid inspired devices. To help achieve a new milestone in biosensing applications, great potential of this emerging technique is described further with regard to sensitivity, specificity, operational convenience, and versatility.