Fabrication of gold nanoparticles based sensors

Abstract

In the first phase of the study we demonstrate a simple chemical route for fabrication of spherical gold nanoparticles (AuNPs) using tranexamic acid as reducing as well as capping agent. Characterization of Tr-AuNPs was carried out via UV-Visible (UV-Vis) spectroscopy and the surface plasmon absorption band was controlled at 522 nm under already optimized conditions. Atomic force microscopy (AFM) unveiled information about size and shape of Tr-AuNPs. Fourier transform infra-red (FTIR) spectroscopy divulged the interaction of capping agent with AuNPs while X-ray diffractometry (XRD) disclosed the nature of crystalline patterns of AuNPs. As-prepared Tr-AuNPs were sandwiched between the surface of glassy carbon electrode (GCE) and nafion to be used as sensor for highly selective and sensitive voltammetric determination of nalbuphine (NA) using square wave voltammetry (SWV) as determining mode. Parameters such as volume of nafion, working electrodes, variety and ionic strength of supporting electrolyte(s), pH, stirring rate, initial potential, accumulation potential, and accumulation time were optimized. The mechanism for the oxidation of NA was also proposed. The sensor responded linearly in the range of 0.05-1.25 µg mL-1 (R2 = 0.997) with excellent limit of detection (LOD) of 13.2 ng mL-1 . The sensor also showed linear calibration plots and lower LODs in regard to NA detection in serum as well as urine samples. The fabricated sensor demonstrates higher selectivity towards sensitive determination of NA in the presence of various interfering species usually found in human serum and urine. The developed sensor was successfully applied and validated for the determination of NA in human serum and urine samples with excellent recoveries. In the second phase, we present a simple and green approach for the synthesis of gold nanoparticles (AuNPs) using analgesic drug, diflunisal (DF) as capping and stabilizing agent in aqueous solution. The characterization of the synthesized diflunisal derived gold nanoparticles (DF-AuNPs) was performed by UV-Visible (UV-Vis) spectroscopy where the surface Plasmon absorption band was found at 520 nm at optimized experimental conditions. Fourier transform infrared (FTIR) spectroscopy established the effective interaction of the capping agent with the VIII AuNPs. Topographical features of the synthesized DF-AuNPs were assessed by atomic force microscopy (AFM) showing average particle height as 29-32 nm. X Ray Diffractrometry (XRD) was used for the study of crystalline nature and it showed excellent crystalline properties of the synthesized DF-AuNPs. The synthesized DF-AuNPs were employed to modify the surface of glassy carbon electrode (GCE) for the selective determination of piroxicam (PX) using differential pulse voltammetry (DPV) technique. The fabricated sensor represented as nafion/DF-AuNPs/GCE, exhibits high sensitivity in comparison to bare GCE. The current response of fabricated sensor was found linearly dependent upon the concentration of PX in the range of 0.5 µM to 50 µM. The limit of detection (LOD) and limit of quantification (LOQ) were determined to be 50 nM and 150 nM respectively. The proposed sensor was successfully utilized for the sensitive and rapid determination of PX in human serum, urine and pharmaceutical samples. In the third phase, we proposed for the first time, gold nanoparticles (AuNPs) based sensor for in vitro assessment of drug-drug interactions (DDIs). Here, we first conducted in-situ molecular docking and simulations studies to interrogate DDIs that allowed predictions of DDIs between two model drugs, such as imipramine (antidepressant) and isoniazid (anti-tuberculosis). This was followed by in vitro studies involving imipramine conjugated gold nanoparticles (Imipramine-AuNPs) as probes for screening DDIs. Association of isoniazid with imipramine molecules over the surface of AuNPs sensor occurred that was confirmed by a combination of physico-chemical methods. Electrochemical investigations revealed the quantitative association of imipramine and isoniazid molecules, where a linear relationship of peak current (Ip) was observed for increasing concentrations of isoniazid from 31 to 667 µM at Imipramine-AuNPs modified Screen Printed Electrodes (SPE), validating the predicted DDIs. The current study aims to highlight the possible interaction between the two drugs that provides valuable information useful for the prediction of similar types of DDIs with other drug pairs. The fourth phase involves dual responsive furosemide functionalized gold nanoparticles (Fr-AuNPs) for colorimetric and electrochemical sensitiveIX determination of dopamine (DP). The synthesized Fr-AuNPs were characterized by UV-Vis spectroscopy, X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and Fourier transform infrared (FTIR) spectroscopy. The Fr-AuNPs were employed as colorimetric probes for the determination of DA. Optical changes in the Fr-AuNPs solution were observed upon addition of DA, revealing the affinity interaction between Fr-AuNPs and DA. The change in absorbance was found to be directly proportional to the concentration of DA in the range of 100 µM to 800 µM. Similarly, an electrochemical sensor was fabricated by immobilization of Fr AuNPs at GCE. The electrocatalytic activity of the Fr-AuNPs was observed as an enhanced oxidation current for DA at Fr-AuNPs/GCE comparison to bare GCE using cyclic voltammetry (CV). Square wave voltammetry (SWV) was found to possess remarkable sensitivity with excellent detection limit of 1 nM of DA at the fabricated sensor. Amperometric measurements also exhibited remarkable catalytic activity for the detection of DA. Linear response was obtained over concentration of DA in the range of 1 µM to 23 µM with detection limit of 0.1 µM. The practical applicability of electrochemical DA sensor was successfully employed for the quantification of DA in human serum and obtained results were found to be satisfactory. The fifth phase reports the voltammetric assay for the simultaneous determination of ascorbic acid and uric acid using isoniazid derived gold nanoparticles (Isn AuNPs) self-assembled on the surface of screen printed electrode (SPE) for the first time. Isoniazid (Isn) was employed to carry out reduction as well as stabilization of gold nanoparticles in aqueous media. The characterization of Isn AuNPs was executed using Scanning electron microscopy (SEM), FTIR spectroscopy and UV-Vis spectroscopy. The resultant Isn-AuNPs were then allowed to attach over the sensing surface of screen printed electrode using L cysteine as linker. The modified SPE demonstrated pronounced catalytic efficiency for oxidation and improved peak separation of around 0.204 V of ascorbic acid and uric acid simultaneously in comparison to bare SPE that showed overlapped peaks for the two analytes. Electrochemical impedance spectroscopy (EIS) was employed to characterize the surface of Isn-AuNPs modified SPE. X Differential pulse voltammetry (DPV) was used to construct linear calibration plots in the concentration range of 10 µM to 50 µM for ascorbic acid and in the range of 3 µM to 10 µM for uric acid and the detection limits were found to be 1 µM and 0.3 µM respectively. The proposed sensing plan was applied for the determination of ascorbic acid and uric acid in human serum and attained results were found to be adequate and could be employed as alternating sensing protocol for the routine analysis of these biological species. The sixth phase consists of synthesis of 5-mercapto-2-nitro-benzoic acid capped AuNPs (MNBA-AuNPs) as sensing probe for the analysis of an anti-psychotic drug prochlorperazine (PRCP). The MNBA-AuNPs were characterized through UV-Vis spectroscopy where the SPR band displayed narrow peak at 521 nm showing controlled size and dispersion. The shape and size of MNBA-AuNPs were determined through scanning electron microscopy (SEM) and the average size of nanoparticles was found to be ~10 nm. The MNBA-AuNPs were immobilized over the surface of GCE that served as sensing platform for the determination of PRCP. Electrochemical impedance spectroscopy (EIS) was used to characterize the interfacial characteristics of the modified GCE. The MNBA-AuNPs/GCE demonstrated enhanced peak currents for the oxidation of PRCP in comparison to bare GCE using cyclic voltammetry (CV). The dependence of peak currents to the concentration was investigated using differential pulse voltammetry (DPV) that demonstrated linearity in the range of 1 to 10 µM and LOD and LOQ were found to be 0.08 µM and 0.2 µM respectively. The proposed method was employed for the determination of PRCP in human serum samples and excellent recoveries were obtained that indicated the applicability of the proposed method for the quantification of PRCP in real samples. The seventh phase consists of the synthesis of paracetamol derived AuNPs (PC AuNPs) for the determination of sulphide. The synthesized PC-AuNPs demonstrated a sharp absorption band at 530 and 722 nm that demonstrated the existence of some anisotropic nanoparticles. Scanning electron microscopy (SEM) was used to examine the morphological features of synthesized AuNPs that displayed different geometries of AuNPs along with spherical nanoparticles. The surface of GCE was modified with PC-AuNPs to examine the cyclic voltammetric XI behavior of sulphide in 0.04 M BR buffer pH 7. The oxidation of sulphide demonstrated sharp anodic peak at 1.0 V at PC-AuNPs/GCE, whereas, no peak was observed at bare GCE indicating the electrocatalytic behavior of PC-AuNPs towards oxidation of sulphide. The pH value of 6 was optimized on account of the highest sensitivity was observed at this pH value. The amperometric measurement for the determination of sulphide was demonstrated in stirred BR buffer pH 6 by consecutive addition of standard solution of sodium sulphide. The current immediately increased upon each addition of sodium sulphide solution with steady state achieved within 5 s. The dependence of current over concentration of sulphide was plotted and two linear relationships were found from 12.5 to 225 µM and 225 to 675 µM. The detection limit was estimated from lower range as 1.2 µM. The proposed method was employed for the determination of sulphide ions in water samples and satisfactory recoveries were observed that indicated the applicability of the proposed method for the determination of sulphide ions in water samples