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Detection of uric acid (UA) is inevitable today, as very less amount of uric acid in human leads to Fanconi Syndrome, Wilson’s disease and cardiovascular disorders. Here, we report an eco-friendly synthesis of a nitrogen-doped carbon dot/Chromium (VI) [N–C dot/Cr (VI)] fluorescent nanoprobe for nanomolar detection of uric acid. N–C dot/Cr (VI) nanoprobe is synthesized using solvent free, fast, easy, green, pyrolysis method, which is characterized using UV–VIS, FTIR, XRD, SEM- EDX and PL technique. Addition of Cr (VI) to fluorescent N–C dot leads to immediate turn OFF in fluorescence with the formation of N–C dot/Cr (VI) nanocomposite. The lowest detection limit of Cr (VI) by N–C dot is 1.42 × 10–9 M. For the first time, we are reporting uric acid, a reducing agent to reduce Cr (VI) to lower valent Cr (III)/Cr (0). The addition of uric acid turns ON the fluorescence with the elimination of inner filter effect (IFE) thus N–C dot/Cr (VI) nanoprobe functioning as a Turn Off–On fluorescent nanosensor for the detection of UA. The efficiency of the sensor is based on fluorescence resonance energy transfer between N-Carbon dots and chromium (VI). A linear response was noted with every nanomolar addition of uric acid. The lowest detection limit toward sensing of UA is found to be 12.5 × 10–9 M. Thus, the novelty of this method is nanomolar amount of redox species is enough to form a stable nanocomposite and the N-CDs/Cr (VI) nanocomposite is able to sense nanomolar to millimolar concentration of uric acid within a few seconds. The nanoprobe is found to be stable, simple and cost effective which can be extended for detection of uric acid in vegetables, fruits and also in clinical studies.

In this work, a new analytical protocol for the selective recognition of NO is described. The mediated reduction of NO by ferrocene forms the basis of analysis. The formation of blue ferrocenyl cation formed as the intermediate during the mediated reduction of NO is confirmed by spectral method and by generating the blue ferrocenyl cation by the chemical oxidation of dichromate in sulphuric acid. The formation of paramagnetic ferrocenyl cation is an interesting feature of this work. Four different methodologies have been followed to incorporate the ferrocene molecules onto the gold electrode surface. The four modified configurations have been evaluated for the selective sensing of NO.

The concept of a bio-inspired oxidation reaction is used along with self-assembled monolayers for the selective recognition of dopamine over ascorbic acid (AA) in this work. Self-assembled monolayers with negatively charged terminal groups are manipulated for selective sensing of dopamine (DA). It is observed that the recognition sensitivity is increased in the mixed monolayer configuration, and this is increased further when copper ions are included in the SAM matrix by chelation. Monolayers of mercaptoundecanoic acid (MUA) and mercaptobenzothiazole (MBT) and mixed monolayers with decanethiol (DT) (viz., DT+MUA and DT+MBT) are used in the present investigations. Good selectivity is observed in the case of the Au/MUA, Au/MUA/Cu2+ and Au/(DT+MUA)/Cu2+ films. The oxidation of AA and DA occurs as two separate peaks in these configurations and hence better recognition is achieved.

In this investigation, the characterisation of monolayer and mixed monolayers formed from mercaptobenzothiazole (MBT) and decanethiol (DT) has been carried out with cyclic voltammetry. The SAMs have been tested for their stability and electron transfer blocking properties. The redox probes used in the present study are [Fe(CN)6]4−, [Ru(NH3)6]2+ and Cu underpotential deposition (upd). The electron transfer kinetics is investigated in acid and neutral pH range. Electron transfer kinetics is altered by the nature of charge on the redox probe and the charge on the monolayer. Electron transfer kinetics of negatively charged redox probes like ferrocyanide ions is blocked when the surface pKa pHmedium reversible features is observed for negatively charged probes. An exactly reverse effect is observed in the case of positively charged redox species like [Ru(NH3)6]2+/3+. Cu under potential deposition studies reflects the structural integrity and compactness of the SAM layer. The utility of these monolayers and mixed monolayer for selective sensing of dopamine is discussed based on their ability to discriminate between positively and negatively charged redox species at different pH.

The present work describes, for the first time, in situ electrochemical preparation of dendrimer-encapsulated Cu nanoparticles using a self-assembled monolayer of fourth-generation amine-terminated polyamidoamine (PAMAM) dendrimer as the template. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) studies of the modified surface confirmed the presence of Cu nanoparticles entrapped in dendrimer film. Au electrode modified with a monolayer of the dendrimer enables preconcentration and subsequent voltammetric detection of Cu(2+) at picomolar concentrations. Further, Cu nanoparticles in the dendrimer monolayer could be electrochemically derivatised to Cu hexacyanoferrate, which exhibits specific crystal planes, unlike the random distribution of crystal planes in bulk-formed Cu hexacyanoferrate, which is another catalytically active material for sensor applications.