| Due to the unique physicochemical properties, sub-nanometre sized metal clusters have already drawn much attention in both fundamental science studies and technological exploration. Increasing interest have been focus on the preparation and application of sub-nanometre sized metal clusters in numerous field especially in bioanalytical chemistry, e.g., chemical sensors, catalysis, biological labeling, bioimaging, and electronics, etc. Fluorescence biosensor-based method is rapid development in applying for biological detection because of its simple preparation, ease of operation, high sensitivity and can be reused. Therefore, the fluorescence biosensor based on metal clusters is particularly important.Alzheimer’s disease (AD) is also known as senile dementia, it is a common progressive neurodegenerative disorder characterized by globalcognitive decline involving memory and judgment.The acetyl-cholinesterase (AChE) in our brain can strong catalyze the hydrolysis of of acetylcholine (ACh), which plays a crucial role in the treatment of AD. In other words, the level of AChE and ACh is highly associated with AD. However, low sensitivity, false-positive effects, complex pre-processing and so on have limited the application of the traditional detection method. So it is essential for developing effective method to realtime monitor the level of choline compounds.In this paper, we synthesize a fluorescent gold nanoclusters (GNCs) as a biosensor for high sensitively detection of choline compounds. In addition, we have developed the proposed method to detect choline compounds in human blood with satisfactory results.The main contents of this paper can be expressed as follows:1. The research found that there were many amino, carboxyl, sulfydryl groups in proteins, they could act as polyvalent ligands for stabilizing the structure of metal atoms, so we could use it as the template to synthesize a fluorescent GNCs. In this part, we denatured a kind of proteins termed lyophilized bovine serum albumin (BSA), BSA had34cysteine residues in the formation of disulfide bonds and only one free cysteine residues. If the disulfide bonds completely liberated, they could act as polyvalent ligands for stabilizing the surface of metallic materials. We examineed if the photoluminescence intensity changed by denaturing the BSA, under different ionic strength environments and long-term stability of gold nanoclusters. The gold nanoclusters we prepared had good dispersion in aqueous solutions, size distrubution of GNCs was1-2nm, whereas they emitted strong red fluorescence under excitation wavelength with520nm.2. Based on the above synthesis method, Here we synthesized simple water-soluble, fluorescent denatured protein-protected gold nanoclusters and then used the gold nanoclusters as a label-free fluorescent sensor for the sensitive and selective detection of AChE activity in human serum. In this paper, S-Acetylth-iocholine iodide (ACTI) was used as the substrate. AChE hydrolyzed ACTI to give thiocholine whose sulfhydryl group can combine with the denatured protein-protected gold nanoclusters leading to fluorescence quenching of the gold nanoclusters. The limit of detection (LOD) was0.02mU mL-1, which was lower than that of previous methods. The protocol was economic, simple, and high sensitivity. 3. Here we reported a simple label-free fluorometric biosensor based on H2O2-sensitive nanoclusters with high sensitivity and selectivity for the detection of acetylcholine. In this paper, AChE could catalyze ACh to produce choline which in turn was oxidized by ChOx to generate H2O2that strongly quenched the fluorescence of the denatured protein-protected gold nanoclusters. On the basis of the specific response, the proposed fluorescence biosensor used for detecting ACh in human blood. The limit of detection (LOD) was5pM, which was lower than that of previous strategies, the proposed method had certain advantages in comparison with the traditional methods in detecting ACh. |
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