Ni 2+-modulated homocysteine-capped CdTe quantum dots as a turn-on photoluminescent sensor for detecting histidine in biological fluids

Abstract

The high affinity of histidine to Ni 2+ has long been recognized in metal ion affinity chromatography for the separation and purification of histidine-tagged proteins. Besides, such affinity pair has been explored in modern nanotechnology for constructing functional nanoparticle-histidine-tagged protein conjugates. However, the use of Ni 2+-histidine affinity pair in conjunction with optically-active nanomaterials for sensor design, to our knowledge, has not been reported yet. Here we report a turn-on photoluminescent sensor for histidine based on Ni 2+-modulated homocysteine (Hcy)-capped CdTe quantum dots (QDs) by taking the advantages of this well-known Ni 2+-histidine affinity pair and photoluminescent QDs. The photoluminescence of Hcy-capped CdTe QDs can be effectively quenched by Ni 2+ due to the binding of Ni 2+ to the Hcy on the surface of the QDs and the electron transfer from the photoexcited QDs to Ni 2+. The high affinity of histidine to Ni 2+ enables Ni 2+ to be dissociated from the surface of Hcy-capped CdTe QDs to form stable complex with histidine in solution, thereby recovering the photoluminescence of Hcy-capped CdTe QDs. The Ni 2+ induced photoluminescence quenching and subsequent histidine-induced photoluminescence recovery for Hcy-capped CdTe QDs build a solid base for the present QD-based turn-on photoluminescent sensor for detecting histidine. The developed QD-based sensor gives excellent selectivity for histidine over other amino acids with the limit of detection (3 s) of 0.3 μM. The relative standard deviation for 11 replicate detections of 15 μM histidine was 2.7%. The developed sensor was applied to the determination of histidine in human urine samples with recoveries from 94.4% to 106%.