Amino acids (AA) have been determined employing quantum dots (QD) as photoluminescent probes for indirect sensing, based on AA-quencher complexation at turn-off-turn-on approaches1,2. The present work aims to evaluation of direct AA sensing by QD and its potential for fast urine analysis. Preliminary assays, using glutathione-coated CdTe QD (GSH-CdTe), were performed against three amino acids groups divided according to their side chains. It was observed that AA with a positive charge or neutral polar chains, namely L-histidine (His) and L-threonine (Thr), promoted a luminescence quenching up to 90% in the GSH-CdTe. Studies on the His-QD binding and quenching mechanism indicated the occurrence of static quenching with the complex association constant (Ksv) varying from 28.1 to 9.7 L/mol due to increasing temperature. Thermodynamic parameters were determined by van't Hoff equations, estimating values of ΔH = -76.5 kJ/mol, ΔS = -227.4 J/K mol and ΔG from -9.8 until -6.4 kJ/mol at 20 to 35 °C. In addition, no variation of Ksv (ΔKsv < 11%) was observed due to the changes in the ionic strength indicating preferentially interactions by Van der Waals forces and/or hydrogen bonding. The evaluation of the interaction parameters showed that in
ammoniacal buffer (0.25 mol/L) at pH 8.0, the QD nanocrystal of 2.2 nm responded only to His with LOD of 1.6x10-4 mol/L. Determination of His was carried out on artificial and human urine with recoveries ranging from 78.7 to 127.6%.