Neha Bhardwaj

Graphene modified screen printed immunosensor for highly sensitive detection of parathion

Due to indiscriminate use of pesticides, there is a growing need to develop sensors that can sensitively detect the trace amount of pesticides in food and water samples. Parathion, identified as an acetylcholinesterase inhibitor, had been one of the most widely used pesticides throughout the world. Symptoms of its poisoning are found to be diverse enough to include nausea, vomiting, diarrhea, muscle cramping/twitching, and shortness of breath. In this work, a graphene based impedimetric immunosensor has been fabricated and employed for highly sensitive and specific detection of parathion. The fabrication proceeded through the modification of the screen-printed carbon electrodes (SPE) with graphene sheets, followed by their functionalization with 2-aminobenzyl amine (2-ABA) via an electrochemical reaction. These amine functionalized graphene electrodes were then bio-interfaced with the anti-parathion antibodies. In the impedimetric mode, this biosensor detected parathion in a broad linear range, i.e. 0.1-1000ng/L with a very low limit of detection (52pg/L). It also showed high selectivity towards parathion in the presence of malathion, paraoxon, and fenitrothion. The viability of this biosensor was demonstrated by detecting parathion in real samples (e.g., tomato and carrot) and through cross-calibration against HPLC.

Immunosensing of Atrazine with Antibody-Functionalized Cu-MOF Conducting Thin Films.

This work reports the assembly of thin films of a silica (SiO2)-modified copper-metal organic framework, Cu3(BTC)2 [Cu3(BTC)2@SiO2, BTC = benzene-1,3,5-tricarboxylic acid] on a conducting substrate of NH2-BDC [NH2-BDC = 2-aminobenzene-1,4-dicarboxylic acid] doped polyaniline (PANI). Assembled Cu3(BTC)2@SiO2/BDC-PANI thin films displayed electrical conductivity in the range of 35 μA. These thin films were conjugated with antiatrazine antibodies to create a novel immunosensing platform. Various structural and spectral characteristics of the synthesized material and its bioconjugate were investigated. The developed immunosensor was used for the conductometric sensing of atrazine. The detection of atrazine was achieved with a high sensor sensitivity (limit of detection = 0.01 nM) and specificity in the presence of diverse pesticides (e.g., endosulfan, parathion, paraoxon, malathion, and monochrotophos).

Bacteriophage conjugated IRMOF-3 as a novel opto-sensor for S. arlettae

This article reports the novel assembly of a bacteriophage-based fluorescent sensor for the selective and sensitive detection of a model bacterium ‘Staphylococcus arlettae (S. arlettae)’. A host specific bacteriophage was bioconjugated with a fluorescence metal organic framework ‘IRMOF-3’. Changes in the photoluminescence intensities of this fluorescent probe were correlated with bacterial concentrations. The proposed bacteriophage based opto-sensor provided a low detection limit (100 cfu mL−1) along with specificity in the detection with respect to other some non-specific bacteria, e.g. S. aureus and E. coli. The detection was achieved over a wide range of bacterial concentrations, i.e. 102–1010 cfu mL−1S. arlettae. Compared to antibody and DNA based optical sensors, the use of bacteriophage in conjugation with IRMOF-3 should offer advantages of simplicity and stability. The use of IRMOF-3 as a fluorescent molecule should also offer the development of reproducible sensors because of its well defined structural geometry and hierarchical assembly.

MOF–Bacteriophage Biosensor for Highly Sensitive and Specific Detection of Staphylococcus aureus

To produce a sensitive and specific biosensor for Staphylococcus aureus, bacteriophages have been interfaced with a water-dispersible and environmentally stable metal-organic framework (MOF), NH2-MIL-53(Fe). The conjugation of the MOF with bacteriophages has been achieved through the use of glutaraldehyde as cross-linker. Highly sensitive detection of S. aureus in both synthetic and real samples was realized by the proposed MOF-bacteriophage biosensor based on the photoluminescence quenching phenomena: limit of detection (31 CFU/mL) and range of detection (40 to 4 × 108 CFU/mL). This is the first report exploiting the use of an MOF-bacteriophage complex for the biosensing of S. aureus. The results of our study highlight that the proposed biosensor is more sensitive than most of the previous methods while exhibiting some advanced features like specificity, regenerability, extended range of linear detection, and stability for long-term storage (even at room temperature).

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).

An overview of different strategies to introduce conductivity in metal–organic frameworks and miscellaneous applications thereof

Metal–organic frameworks (MOFs) are known to possess many interesting material properties such as high specific surface area, tailorable porosity, adsorption/absorption capabilities, post-synthetic modifications, and chemical/thermal stabilities. Because of these unique features, they have been explored for the development of sensors for a variety of analytes. A large proportion of pre-existing MOF-based sensors are well suited for optical transductions due to a lack of electrical conduction in their pristine forms. Hence, the development of MOF-based electrochemical/electrical sensors requires specialized strategies through which MOFs are modified or hybridized with enhanced conductive moieties (e.g., via doping or post synthetic modification). In this review article, we provide a comprehensive review of various synthetic and integrating strategies to improve electrical conductivity and long-range charge transport properties in MOFs. To this end, we have compiled details of different techniques that have been used to develop electrically/electrochemically active platforms for MOF-based sensing of various targets.