Search

This study presents the development of an efficient and cost-effective voltammetric sensor for the individual and simultaneous determination of uric acid (UA), tryptophan (Try) and hypoxanthine (HX), the three important biomarkers in the human body. The sensor consists of glassy carbon electrode (GCE) modified with the conducting layer of poly(L-Arginine) (p-Arg) prepared by the electropolymerisation of L-Arginine using cyclic voltammetry. p-Arg modified GCE (p-Arg/GCE) provided well-resolved and improved electrooxidation responses for UA, Try, and HX due to the greater electrocatalytic activity and fast electron transfer ability of the polymer layer. The fabricated sensor was characterised using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Atomic Force Microscopy (AFM), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Electrochemical Impedance Spectroscopy (EIS) and electroactive surface area calculations. Under optimal analytical conditions, determination of the three analytes was possible over wide linear ranges with the limit of detection of 1.97 × 10−8M, 4.43 × 10−8M, and 8.44 × 10−9M, respectively for UA, Try, and HX. Practical utility of the sensor was successfully verified in synthetic urine and blood serum samples and determination of Try and HX was carried out in dietary supplements and commercially available samples of tea and coffee, respectively.

Serotonin (ST), chemically 5-hydroxy tryptamine, is a neurotransmitter which mediates a series of central and peripheral functions in the human body and has a crucial role in gastrointestinal and psychiatric disorders. Tryptamine (Tryp) is also a neurotransmitter, mainly found in protein-rich foods, beverages and other fermented foods. The accumulation of higher concentrations of Tryp is harmful to human health. So, it is important to determine both ST and Tryp in our body. A polyglutamic acid (pGlu)-Silver Nanoparticles (AgNPs) composite film modified Glassy Carbon Electrode (pGlu-AgNPs/GCE) has been developed for the simultaneous determination of ST and Tryp. The incorporation of AgNPs with pGlu makes the sensor more efficient and reliable for the voltammetric sensing of ST and Tryp. Experimental parameters were optimised and, the sensor showed a linear concentration range for the determination of ST and Tryp from 1.00 × 10–5M to 7.00 × 10–7M and 1.00 × 10–5M to 9.00 × 10–7M, respectively. The electrooxidation of ST at pGlu-AgNPs/GCE was found to be diffusion controlled, whereas adsorption controlled electrooxidation was found for Tryp. The applicability of the sensor in determining ST and Tryp has been checked in artificial physiological fluids.

Apart from the significant physiological roles of hormones and purine metabolites in higher level living organisms, these biomolecules act as recognised biomarkers for early disease detection and its periodical monitoring. This article details the development of a voltammetric sensor based on a copolymer of [L-Cystein (LCys) and 2-(N-morpholino)ethanesulfonic acid (MES)] modified glassy carbon electrode for the selective and sensitive determination of Epinephrine (EP), Uric acid (UA), Xanthine (XA) and Hypoxanthine (HX) individually as well as simultaneously. Different perspectives of electrocopolymer formation and involved reaction mechanisms have been investigated and substantiated via Cyclic voltammetry, ATR and Raman spectroscopy. This copolymer modification enables the formation of well-defined peaks for the analytes and under optimised conditions, the designed sensor possess wide linear range with limit of detection of 9.22 × 10−7M, 5.147 × 10−7 M, 1.260 × 10−7 M and 2.406 × 10−7 M for EP, UA, XA and HX respectively. Scan rate studies were well employed to derive the mechanistic aspects behind the electrooxidation reactions. The credibility in measurements were validated via repeatability, reproducibility and stability studies. Also, the feasibility of the proposed sensor was examined in real samples and the obtained results were validated via traditional analytical techniques which demonstrates its practical utility in real time monitoring.

Neuroendocrine tumours are cancerous and fatal lumps that originate from endocrine and nerve cells. Herein we report the first voltammetric sensor for the simultaneous determination of neuroendocrine tumour biomarkers 5-Hydroxy indole acetic acid (HIAA) and Vannillyl mandelic acid (VMA). Glassy carbon electrode modified with a copolymer of taurine and glutamic acid by electropolymerisation process has been used for the determination of the analytes. The synergistic effect of the two conducting polymers gave remarkable voltammetric response for the biomarkers. Calibration measurements for the sensor were carried out using fast and feasible square wave voltametric technique. Detection limits as low as 4.19 × 10−8M (HIAA) and 6.16 × 10−8 M (VMA) is possible with this voltammetric sensor with only tolerable interference from their coexisting species. To boot, spike recovery analysis of the analytes in artificial urine samples gave adequate recovery values, which proves the reliability of the sensor.

An effective electrochemical sensor based on “poly L- methionine/Electrochemically Reduced Graphene Oxide Composite Film Modified Glassy Carbon Electrode (poly(L-Met)/ERGO/GCE))” has been developed for the individual and simultaneous determination of 5-hydroxyindole acetic acid (5-HIAA) and tyrosine (Tyr). In clinical point of view, simultaneous determination of these analytes is very important and a sensor for the same is not reported yet. This sensor offers sensitive, reproducible and selective determination of 5-HIAA and Tyr. Experimental parameters for the effective determination of the analytes were optimized. Under optimized conditions, quantification of 5-HIAA is possible within the range 1.0 × 10−5 M to 8.0 × 10−7 M and for Tyr in two ranges, 1.0 × 10−5 M to 5.0 × 10−6 M and 7.0 × 10−5M to 2.0 × 10−5M. The limit of detection and limit of quantification obtained for 5-HIAA using poly(L-Met)/ERGO/GCE are 5.0 × 10−7 M and 8.0 × 10−7 M respectively, and for Tyr, 1.0 × 10−6 M and 5.0 × 10−6 M respectively. The sensor was successfully applied for the determination of both 5-HIAA and Tyr in artificial urine and blood serum samples.

The electrooxidation of acyclovir (ACV) was studied using a gold electrode (GE) modified with a self-assembled monolayer of 2-mercaptobenzothiazol (MBZ) and [5,10,15,20-tetrakis(3-methoxy-4-hydroxyphenyl)porphyrinato]-copper(II) (TMHPP Cu(II)) by square wave voltammetry (SWV). The self-assembled films are stable and showed blocking characteristics towards the faradaic processes such as gold surface oxidation and under potential deposition of copper. The optimized conditions obtained for the MBZ/TMHPP Cu(II)-modified GE were 0.1 M phosphate buffer solution (pH 7.0), square wave frequency of 15 Hz and square wave amplitude of 25 mV. Under these optimum conditions, the resultant peak current increases linearly with the concentration of ACV in the range of 1.0 × 10–3to 1.0 × 10–8M with a detection limit of 1.0 × 10–8M. The MBZ/TMHPP Cu(II)-modified GE showed good stability and selectivity and it can be used to quantify ACV in pharmaceutical formulations and urine samples.

A PVC membrane sensor for the selective determination of mebendazole (MBZ) was fabricated. The sensor is based on an ion association of MBZ with silicotungstic acid (STA) as ion pair and bis(2-ethylhexyl)phthalate (BEP) as the plasticizing agent in a PVC matrix. The sensor showed a linear response for MBZ for a concentration range 1.0 × 10-6- 5.0 × 10-2M with a Nernstian slope of 55.8 mV/decade (limit of detection 6.3 × 10-7M) in the pH range 4 - 7. It has a fast response time of <30 s. The sensor showed a very good selectivity for MBZ with respect to a large number of ions. The direct determination of MBZ in pharmaceutical formulations gave results that compare well with the data obtained from the standard method.

A new series of hepta coordinated lanthanide(III) complexes of the type [ML2Cl3] (where M = LaIII, PrIII, NdIII, SmIII, GdIII, TbIII, DyIIIor YIII, L = trimethoprim) have been synthesised. The new complexes were characterised using various physico-chemical methods such as elemental analysis, spectral (IR, UV–VIS, 1H NMR), magnetic and X-ray diffraction analysis. A monocapped trigonal prism structure has been tentatively proposed for the complexes.

The article details the development of a poly(para amino benzene sulfonic acid) modified glassy carbon electrode as a sensor for simultaneous determination of purine bases; guanine, adenine and uric acid. When 0.1 M NaOH was used as the supporting electrolyte the electro-oxidation of these analytes took place at well resolved electrode potentials which facilitated their simultaneous determination without any electrode fowling. The sensor response has been calibrated for both simultaneous and individual determination. Wide linear working concentration ranges and good detection limits were obtained for both. The selectivity of the sensor for simultaneous determination has been checked among these purine bases as well as in the presence of other possibly co-existing species. The sensor has been demonstrated to be efficient for determination of uric acid, guanine and adenine in acid denatured herring sperm DNA. The mechanistic and kinetic parameters such as charge transfer coefficient, number of electrons involved in the rate determining step, diffusion coefficient and heterogeneous rate constant for the electro-oxidation of these bases on the poly(para amino benzene sulfonic acid) modified glassy carbon electrode has also been determined.

A gold electrode (GE) modified with L-cysteine and gold nanoparticles (AuNPs) has been generated for computing the individual and simultaneous determination of nimesulide (NM) and acetaminophen (APAP). The electrochemical behavior of the pair of molecules has been inspected utilizing square wave voltammetry (SWV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Studies indicated that the oxidation of APAP and NM is expedited at AuNPs/L-cysteine GE giving well defined peaks for APAP and NM at 0.596 V and 1.072 V respectively in Britton-Robinson (B-R) buffer (pH 2). The assay enabled simultaneous determination of these drugs in the linear working range of 3.0 × 10−4M–1.0 × 10−5M with detection limits of 4.06 × 10−7M and 6.49 × 10−6M for APAP and NM respectively. The high selectivity and sensitivity of the proposed assay were illustrated by its active application in the ascertainment of both APAP and NM in pharmaceutical preparations.