Ankan Dutta Chowdhury

Non-enzymatic electrochemical detection of cholesterol using β-cyclodextrin functionalized graphene

A non-enzymatic approach towards cholesterol detection is presented here, exploiting the electrochemical non-enzymatic route of sensing which has a distinct advantage over other conventional enzymatic processes. Chemically converted Graphene modified with β-CD, being hydrophilic, electroactive and high surface area material, provides a platform for the electrochemical detection of cholesterol using Methylene Blue as redox indicator. Methylene Blue (MB) forms an inclusion complex with Grp-β-CD and emerges as a cholesterol sensing matrix. MB molecule is replaced by cholesterol molecule and moves out in the buffer solution, hence, detected electrochemically using Differential Pulse Voltammetric (DPV) technique. The sensing matrix is characterised using FT-IR and Raman spectroscopy. Transmission Electron Microscopy is carried out to study the morphology of functionalized graphene sheets.

Label-Free and Nondestructive Separation Technique for Isolation of Targeted DNA from DNA–Protein Mixture Using Magnetic Au–Fe3O4 Nanoprobes

The interest in DNA-protein-based diagnostics has recently been growing enormously, which makes the separation process of DNA or protein from a cell extract extremely important. Unlike the traditional separation process, a novel approach is in demand which can nondestructively isolate the target biomolecules without sacrificing the other components in the mixture. In this study, we have demonstrated a new and simple separation technique by using well-established bifunctional Au-Fe3O4 nanocomposites as the separation nanoprobes to efficiently isolate the specifically targeted nanomolar concentrated DNA over 70% from its associate DNA-protein mixture in the presence of a magnetic field. The sensing accuracy of both as-separated DNA and protein are quantitatively examined by UV-vis spectroscopy, and then qualitatively validated by gel analysis. Results obtained in this study clearly demonstrated that this newly developed separation procedure not only provides the efficient separation for the targeted DNA but can also maintain the bioactivity of as-separated protein and DNA solutions. The superiority of this technique can open an avenue to establish a label-free and nondestructive platform for a wide variety of biomolecule separation applications.

N-Doped Graphene Quantum Dots-Decorated V2O5 Nanosheet for Fluorescence Turn Off–On Detection of Cysteine

The development of a fast-response sensing technique for detection of cysteine can provide an analytical platform for prescreening of disease. Herein, we have developed a fluorescence turn off-on fluorescence sensing platform by combining nitrogen-doped graphene quantum dots (N-GQDs) with V2O5 nanosheets for the sensitive and selective detection of cysteine in human serum samples. V2O5 nanosheets with 2-4 layers are successfully synthesized via a simple and scalable liquid exfoliation method and then deposited with 2-8 nm of N-GQDs as the fluorescence turn off-on nanoprobe for effective detection of cysteine in human serum samples. The V2O5 nanosheets serve as both fluorescence quencher and cysteine recognizer in the sensing platform. The fluorescence intensity of N-GQDs with quantum yield of 0.34 can be quenched after attachment onto V2O5 nanosheets. The addition of cysteine triggers the reduction of V2O5 to V4+ as well as the release of N-GQDs within 4 min, resulting in the recovery of fluorescence intensity for the turn off-on detection of cysteine. The sensing platform exhibits a two-stage linear response to cysteine in the concentration range of 0.1-15 and 15-125 μM at pH 6.5, and the limit of detection is 50 nM. The fluorescence response of N-GQD@V2O5 exhibits high selectivity toward cysteine over other 22 electrolytes and biomolecules. Moreover, this promising platform is successfully applied in detection of cysteine in human serum samples with excellent recovery of (95 ± 3.8) - (108 ± 2.4)%. These results clearly demonstrate a newly developed redox reaction-based nanosensing platform using N-GQD@V2O5 nanocomposites as the sensing probe for cysteine-associated disease monitoring and diagnosis in biomedical applications, which can open an avenue for the development of high performance and robust sensing probes to detect organic metabolites.