Impedimetric and Plasmonic Sensing of Collagen I Using a Half-Antibody-Supported, Au-Modified, Self-Assembled Monolayer System

This research presents an electrochemical immunosensor for collagen I detection using a self-assembled monolayer (SAM) of gold nanoparticles (AuNPs) and covalently immobilized half-reduced monoclonal antibody as a receptor; this allowed for the validation of the collagen I concentration through two different independent methods: electrochemically by Electrochemical Impedance Spectroscopy (EIS), and optically by Surface Plasmon Resonance (SPR). The high unique advantage of the proposed sensor is based on the performance of the stable covalent immobilization of the AuNPs and enzymatically reduced half-IgG collagen I antibodies, which ensured their appropriate orientation onto the sensor's surface, good stability, and sensitivity properties. The detection of collagen type I was performed in a concentration range from 1 to 5 pg/mL. Moreover, SPR was utilized to confirm the immobilization of the monoclonal half-antibodies and sensing of collagen I versus time. Furthermore, EIS experiments revealed a limit of detection (LOD) of 0.38 pg/mL. The selectivity of the performed immunosensor was confirmed by negligible responses for BSA. The performed approach of the immunosensor is a novel, innovative attempt that enables the detection of collagen I with very high sensitivity in the range of pg/mL, which is significantly lower than the commonly used enzyme-linked immunosorbent assay (ELISA).

A cost effective strategy for dual channel optical sensing of adrenaline based on 'in situ' formation of copper nanoparticles

Assessment of adrenaline (ADR) levels in biological fluids and pharmaceutical formulations is of prime importance due to its association with many disease conditions. Here a novel, cost effective, dual channel sensing strategy is developed for ADR based on in situ formation of copper nanoparticles. The proposed sensor works via both fluorimetry and colorimetry. Visual detection was also enabled by color change of solution from pale blue to reddish brown. Here CuCl₂ solution is used as probe to simplify method and was function as excellent fluorimetric as well as colorimetric ADR sensor. Fabricated sensor is very simple, selective and reproducible in nature. Proposed sensor works fluorimetrically in linear range of 3.00 × 10^-5 to 5.00 × 10^-7 M and colorimetrically in linear range of 5.00 × 10^-4 to 2.00 × 10^-5 M. Artificial urine and commercial pharmaceutical formulations were successfully analyzed as samples for estimation of ADR by developed dual channel sensor.

Interaction of tetracycline with l-cysteine functionalized CdS quantum dots - Fundamentals and sensing application

The present paper reports l-cysteine functionalized CdS quantum dots (QDs) as a simple and highly selective turn-off fluorescence sensor for the determination of tetracycline (TET). The unauthorized use of TET may pose serious health hazards in human beings and hence the detection and determination has become very essential. In this regard, we have developed a sensor that enable the quantification of TET in the range 6.00 × 10^-4 M to 1.50 × 10^-5 M with a limit of detection 7.78 × 10^-6 M, under optimized conditions. Steady state and time resolved fluorescence spectroscopic studies were used for investigating the mechanism of quenching and was found to be a combination of static and dynamic processes. The analytical application of the proposed sensor was investigated in pharmaceutical formulation.

Copper nanoclusters: an efficient fluorescence sensing platform for quinoline yellow

Fluorescence quenching behavior of artificial food colorant quinoline yellow (QY), on interaction with l-cysteine stabilized copper nanoclusters (l-Cys-CuNCs) is investigated in this work. For this purpose, l-cysteine stabilized CuNCs were synthesized and characterized using various analytical techniques. Results demonstrated that the synthesized probe (size ~2 nm) had very promising optical features such as bright blue fluorescence, significant quantum yield and excellent photostability. l-Cys-CuNCs can function as a fluorescence sensor by selectively sensing QY among other yellow colorants, giving a detection limit as low as 0.11 μM. The developed sensor exhibited a linear concentration range from 5.50 to 0.20 μM. The developed fluorescence assay was successfully applied for testing commercial samples, thereby making this sensing strategy significant for quality control of food stuffs.

Fluorescence Determination of Glutathione Using Tissue Paper-derived Carbon Dots as Fluorophores

Glutathione is an important antioxidant found in body fluids and tissues, which inhibit damage to essential cellular constituents caused by reactive oxygen species. The analysis of glutathione levels in biological systems is important in early clinical diagnosis. A novel, cost-effective synthetic strategy has been developed for the fluorescent probe ethylenediamine passivated carbon dots. Tissue paper was chosen as the carbon source for this "green one pot" synthesis. Glutathione could induce quenching of the fluorescence intensity of ethylenediamine passivated carbon dots through surface interactions, resulting from their aggregation. Based on this, a novel fluorescence sensor was fabricated for the determination of Glutathione in body fluids. A linear calibration graph was obtained in the range of 6.0 × 10^-7 to 5.0 × 10^-8 M with a detection limit of 1.74 × 10^-9 M. The developed sensor was successfully used for the determination of glutathione in artificial saliva samples.

Biothiols induced colour change of silver nanoparticles: A colorimetric sensing strategy

A sensor for the detection and determination of bio-thiols (glutathione (GSH) and cysteamine (Cyste)) has been developed by integrating the distinguished distance related optical characteristics of silver nanoparticles with the simplicity of colorimetric technique. In presence of these analytes, shift in surface plasmon resonance (SPR) absorption of silver nanoparticles (AgNPs) with change in its colour was observed. Yellow coloured AgNPs solution becomes colourless in presence of GSH and changes to red in presence of Cyste. FTIR, TEM and DLS studies were used to confirm the mechanism. The difference in absorption of AgNPs in the absence and presence of GSH was found to vary linearly in the range 1.00×10^-5M to 5.00×10^-7M concentration range with limit of detection at 3.68×10^-7M. The method can also be applied to quantify Cyste in the range 1.10×10^-6M to 5.00×10^-8M with limit of detection at 1.80×10^-8M. The utility of the proposed colorimetric assay is validated by determination of GSH and Cyste in artificial blood serum.

Selective recognition of creatinine - Development of a colorimetric sensor

The present report describes a simple and cost effective protocol for colourimetric determination of creatinine (CR), L-cysteine stabilized copper nanoparticles (L-cys-CuNPs) exhibited selective and sensitive interaction with CR. Utilizing this interaction, a colourimetric sensor has been developed based on the reduction in LSPR intensity as monitored by a UV-visible spectrophotometer. The developed sensor exhibited a linear dynamic range of 5.33 × 10^-6 to 3.33 × 10^-7 M. Proposed sensor is simple and cost - effective compared to methods based on noble metal nanoparticles and the sensitivity to determine CR was as low as 4.54 × 10^-10 M. The sensor was successfully applied for quantification of CR in artificial serum and urine samples. Sensor developed in this work has a high potential for rapid and on-site determination of CR in physiological and clinical samples.

Fluorescence Turn off Sensor for Brilliant Blue FCF- an Approach Based on Inner Filter Effect

A nanosensor with fluorometric readout based on L-cysteine capped cadmium sulphide quantum dots for discriminative detection and determination of Brilliant blue FCF (BB) (in 0.5 M Tris buffer solution of pH 9.5) over other synthetic food colourants is developed. Mechanism of the nanosensor is based on inner filter effect (IFE). The addition of BB into quantum dot solution might induce the quenching of fluorescence. The nanosensor described in this report reveals its simplicity and flexibility due to less laborious and more cost-effective synthesis. The developed fluorescence sensor showed excellent selectivity towards BB, and allows the detection as low as 3.50 × 10^-7 M. The developed sensor exhibited a linear concentration range of 4.00 × 10^-5 to 4.50 × 10^-6 M. More importantly, the proposed sensor exhibit sensitive responses toward BB in food samples such as sports drink and candies, demonstrating its potential in food analysis, which might be significant in food quality control in the future.