Direct colorimetric detection of aspartic acid in rat brain based on oriented aggregation of Janus gold nanoparticle

We report a colorimetric assay based on oriented Janus gold nanoparticles (AuNPs) aggregation for highly selective and sensitive detection of aspartic acid (Asp) in rat brain. Initially, the Janus AuNPs with relatively large size was prepared, during which the stabilizing agent polyethylene glycol (PEG) and highly selective recognition agent cysteine (Cys) were attached to the selected area at the surface. The addition of Asp causes the oriented and controllable aggregation due to the specific recognition between Cys and Asp. Such a way of aggregation leads to significantly improved long-term stability and an at least 2 orders of magnitude wider dynamic range (1.8 nM-180 mu M) compared with conventional colorimetric sensors. In addition, the strategy to increase the size of AuNPs (13-45 nm) enables to efficiently increase the limit of detection (18 mu M-1.8 nM). Surprisingly, such a sensor can be applied to direct sensing of cerebral Asp in rat brain, which is determined round 33.9 +/- 1.3 mu M with satisfactory spiked recovery (86.5 +/- 7.5%) due to the excellent anti-interference ability. This work provides a direct and reliable method to evaluate the Asp involved physiological and pathological process and opens a new avenue for real sample detection.