Evaluation of the Direct Interaction between Amino Acids and Glutathione-Coated CdTe Quantum Dots and Application in Urinalysis for Histidine Determination

The present work aimed to direct amino acid (AA) sensing by quantum dots (QD) and development of an analytical method for potential fast clinical tests. Notably, AA with a positive charge or neutral polar chains, namely L-histidine (His) and L-threonine (Thr), responded to glutathione-coated CdTe (GSH-CdTe) ( Δ F ≤ 90%, variation of fluorescence intensity). However, in ammoniacal buffer (0.25 mol L-1) at pH 8.0, 2.2 nm GSH-CdTe responded only to His. Static quenching with complex association constant (Ksv) varying from 2.81 to 0.94 (10 L mol-1) as well as van der Waals forces and/or hydrogen bonding were predicted for His-QD quenching mechanism and binding type. Additionally, thermodynamic parameters as Δ H = -76.5 kJ mol-1 (enthalpy), Δ S = -227.4 J K-1 mol-1 (entropy) and Δ G from -9.8 until -6.4 kJ mol-1 (Gibbs free energy) at 20 to 35 °C were estimated by van ’ t Hoff equation. Under optimal conditions, the developed method presented a linear range from 0.42 to 35 mmol L-1 (with correlation coefficient (r) of 0.9970, n = 7), good precision (relative standard deviations (RSD)< 2.5% for 2.5 and 20 mmol L-1; n = 6) and limit of detection 1.6 × 10-4 mol L-1 (0.025 mg mL-1). Recovery tests were performed on artificial urine and human urine samples with recoveries ranging from 78.7 to 127.6%.
Source: Journal of the Brazilian Chemical Society - Category: Chemistry Source Type: research