Eilctrochemical Analysis For Determination Of Plasma Indole: Clinical Application In Patients With Gestational Diabetes Mellitus

Objective:1.To establish a sensitive and rapid method for the direct electrochemical detection of indole and explore its reaction principle.2.To establish an electrochemical sensor for plasma indole based on multi-walled carbon nanotubes(MWCNTs)-chitosan(CS)modified screen-printed carbon electrode(SPCE).3.The clinical application of electrochemical analysis for the detection of plasma indole in healthy pregnant women and patients with gestational diabetes mellitus(GDM),to investigate the change of indole in disease.Methods:1.Taking advantage of the ability to oxidize the carbon-carbon double bonds in the imidazole ring of indole,cyclic voltammetry(CV)and differential pulse voltammetry(DPV)were used to analyze indole qualitatively and quantitatively.2.The MWCNTs-COOH was added into the CS solution and the mixture was treated by ultrasonic to form a homogeneous MWCNTs-CS suspension solution.The particles in the suspension were subsequently removed by centrifugation,the dispersion was dropped on the surface of the SPCE and dried at room temperature for preparation of MWCNTs-CS/SPCE.Plasma samples were mixed with PBS solution after liquid-liquid extraction,and then the solution was dripped onto the surface of the SPCE and measured by DPV.3.The above-established MWCNTs-CS/SPCE was applied to the analysis of plasma indole in 21 healthy pregnant women and 21 patients with gestational diabetes mellitus(GDM).In addition,the clinical data and laboratory index were collected.Results:1.According to the adsorption isotherm and the Nernst equation,a total of two electrons and two protons were lost in the electrochemical oxidation of indole.Under the optimized conditions,the linear range of indole was from 0.125 to 10.0 mg/L,the regression equation was y=0.3615x-0.0537(R~2=0.9984)with the detection limit of 25?g/L(S/N=3).The intraday and interday variations were lower than 4.3%and 5.5%respectively,and the average recoveries were 80.6%-126.9%.2.Under the optimized conditions,the linear range of plasma indole was from 5 to 100?g/L,the regression equation was?I=0.0228c+0.3007(R~2=0.9905)with the detection limit of 0.5?g/L(S/N=3).The intraday and interday variations were lower than 7.3%and 9.0%respectively,and the average recoveries were 93.8%-107.0%.The plasma concentrations of indole in 24 cases were simultaneously determined by this method and the high performance liquid chromatography.The correlation analysis showed the results had a significant positive correlation(r=0.886,p=0.000)3.The concentrations of plasma indole in healthy pregnant women and GDM patients were 5.3(4.1–7.0)?g/L and 7.2(4.5–9.4)?g/L,respectively.The plasma indole concentration in GDM patients was significantly higher than that in normal controls(P<0.05).The level of fasting insulin and HOMA-IR in GDM patients were significantly higher than those in normal controls(P<0.001).It was found that plasma indole concentration was positively correlated with TG in all subjects(r=0.312,p=0.044),and was negatively correlated with HOMA-IR in patients with GDM(r=-0.364,p=0.022).Conclusions:1.The direct detection of indole by unmodified SPCE has satisfactory sensitivity and reproducibility.It has a good application prospect in the manufacture of indole electrochemical sensors.2.The developed sensor provided a promising way for the quantitative detection of indole in plasma with better sensitivity,stability and higher reproducibility than unmodified SPCE in clinics.3.It was found that there was an indole metabolic disorder in the GDM,suggesting that indole may play an important role in the development of GDM.