Sensitive detection of butyrylcholinesterase activity based on a separation-free photothermal assay

•A separation-free photothermal assay was developed for the detection of BChE activity.•The sensitive detection of BChE is achieved, achieving a LOD as low as 40.65 U/L.•The photothermal features of polydopamine nanoparticles was tuned by MnO2 nanosheets. Butyrylcholinesterase (BChE), a regulator for the cholinesterase activity in serum, is an important index for clinical diagnosis of organophosphorus poisoning and liver related disease. However, the assays for BChE activity are highly dependent on expensive and bulk equipment and professional operators, which limits its straightforward and portable detection. In this work, we proposed a straightforward and sensitive photothermal assay for the detection of BChE activity, avoiding the use of expensive instrument, professional operators, and separation process. Polydopamine (PDA) nanoparticles can be produced through the oxidation of dopamine by MnO2 nanosheets, which show a rather strong photothermal features. Hydrolyzation of substrate into thiocholine and butyrate happens after introducing BChE. The generated thiocholine and butyrate inhibit the formation of PDA nanoparticle through reducing MnO2 into Mn2+ and creating an acidic environment, respectively. Those effects lead to the decreasing of photothermal efficiency of the reaction system, resulting in the decreasing on temperature change. Quantitative detection of BChE activity is achieved by recording the temperature change of system, using a common device, with a limit of detection of 40.65 U/L calculated. The presented results provide a clue for developing straightforward and portable photothermal assay for BChE, which shows great potential for their clinical applications.