Electrochemical sensing of limonene using thiol capped gold nanoparticles and its detection in the real breath sample of a cirrhotic patient

Abstract

• Molar ratio of gold salt to thiol compound (2:1) synthesised best performing AuNPs. • Hexanethiolated capped AuNPs electrochemically detected limonene (LOD= 0.2 mmol L −1 ). • Limonene was detecteded in a cirrhotic patient breath sample using Hexanethiolated capped AuNPs. • Quantitative electrochemical detection of limonene was confirmed vusing GCMSto be 800 ppm. Volatile organic compounds (VOCs) are a major constituent of human breath which is being investigated as potential targets to be sensed in e-nose biosensors. Limonene is found in the breath of cirrhotic liver patients and can be used for early diagnosis using electrochemical biosensors. In the current study, electrochemical detection of limonene was performed using monolayer thiolated gold nanoparticles. Three different types of monolayer thiol capped AuNPs were synthesized by the modified biphasic method with the different molar ratios (2:1 and 1:1) of hydrogen tetrachloroaurate (III) (HAuCl 4 ·2H 2 O) and thiol groups: dodecanethiol, decanethiol, and hexanethiol. Thiol capped AuNPs were characterized physiochemically and for electrochemical sensing at different factors such as pHs, scan rate, current stability. Based on the best presented electrochemical results, hexanethiol AuNPs were selected as a sensor for analyzing the electrochemical detection of limonene as an analyte. Hexanethiol capped AuNPs based biosensing platform showed high sensitivity with a LOD of 0.2 mmol L −1 as observed via its DPV, and high specificity when was used against another VOC standard. The sensor was also used to detect limonene in the real breath sample of the clinical patient, besides testing the lab standard of limonene. The breath sample of cirrhotic patients was collected and tested for the presence of limonene by using GC–MS. The quantity of limonene measured via GC–MS was 800 ppm in cirrhotic patients and electrochemical sensor measurements of limonene were almost the same providing confidence over quantitative detection of the synthesized hexanethiol capped AuNPs based biosensing platform in this study.