The interaction of skin sensitizers with gold nanoparticles and cysteine modified screen printed carbon electrode analyzed using impedance technique

Abstract

Skin sensitization is defined as an allergic response to a skin sensitizer upon contact with the skin. Skin sensitization is induced through covalent binding of a skin sensitizer to skin proteins (haptenation process). Skin sensitization is usually studied using wet chemistry method. Previously, surface plasmon resonance (SPR) was used to study skin sensitization to speed up the analysis but SPR biosensor was costly and is less sensitive towards low molecular weight compounds. Due to the limitation of using SPR technology for skin sensitizer analysis, the use of disposable screen printed carbon electrode (SPCE) modified with gold nanoparticles (AuNPs) and cysteine, analyzed using electrochemical impedance spectroscopy (EIS) has been proposed. The objective of this study was to investigate the interaction of skin sensitizers with AuNPs and cysteine modified SPCE using impedance technique. EIS was carried out to measure the changes in charge transfer resistance of skin sensitizer (ΔRCTskin sensitizer) as a result of different binding rates of affinity skin sensitizers to cysteine. SPCE modified through electrodeposition of AuNPs/thiourea/self–assembly of AuNPs/cysteine (designated as ETSC) was selected as the best electrode for the detection of skin sensitizers. Investigation on the effect of potency of skin sensitizers on ΔRCTskin sensitizer readings suggested that ΔRCTskin sensitizer readings were directly proportional to the strength of the skin sensitizers with strong/extreme skin sensitizers displaying higher ΔRCTskin sensitizer readings compared to moderate and weak/non skin sensitizers. Fractional coverage area (θPIS) of ETSC modified SPCE exposed with maleic anhydride (extreme/strong sensitizer) was estimated as 0.98 with ra and 2rb of 2.50 µm and 15.99 µm, respectively. The θPIS for ETSC modified SPCE exposed with isoeugenol (moderate sensitizer) and glycerol (weak/non sensitizer) were estimated as 0.9536 and 0.8757, respectively with ra and 2rb of 4.73 µm and 21.96 µm; and 7.08 µm and 40.20 µm, respectively. Kinetic study showed that adsorption of skin sensitizers on ETSC modified SPCE followed Langmuir isotherm with a binding rate constant of 5.00×10+03 M-1 for maleic anhydride, 2.00×10+03 M-1 for isoeugenol and 1.67×10+02 M-1 for glycerol. The interaction of the skin sensitizers to the ETSC modified SPCE was probed using Fourier transform infrared spectroscopy and atomic force microscopy method and the results showed discernible differences between different classes of skin sensitizers. The data obtained from human analysis, this work, human cell line activation test (h–CLAT), direct peptide reactivity assay (DPRA), KeratinoSensTM and SPR biosensor matched the categorization of local lymph node assay (LLNA–a gold standard in skin analysis testing) in the following descending order: 96 %, 92 %, 82 %, 70 % (DPRA and KeratinoSensTM) and 12 %. With only 8 % mismatched with the data obtained using LLNA, EIS method employing ETSC modified SPCE used in this research has the potential to be employed as a screening tool for the identification of skin sensitizers.