Detection of leucine aminopeptidase activity in serum using surface-enhanced Raman spectroscopy.

Leucine aminopeptidase (LAP), an important proteolytic enzyme, is closely associated with diverse physiological and pathological disorders such as liver injury and cancers. Hence, it is imperative to develop an effective method to detect LAP activity for early diagnosis of diseases. In this work, we report a novel SERS probe bis-s-s'-[(s)-2-amino-N-(3-thiophenyl)-Leu]. (b-(s)-ANT-Leu) with an l-leucine amide group, which can specially respond to LAP, to assay the LAP activity according to the SERS spectral changes between the probe molecule and its corresponding hydrolysis product resulting from the catalysis of LAP. This SERS approach features high selectivity on account of the specificity of the reaction combined with the instinctive fingerprinting ability of SERS and shows a good linear relationship in a wide range from 0.2 to 100 mU mL-1 with a detection limit as low as 0.16 mU mL-1. In addition, the SERS-based strategy can be competent for LAP activity detection in clinical patient serum samples and LAP inhibitor evaluation, demonstrating its great potential in the pathological analysis for diseases involving LAP and the screening of LAP inhibitors.

A phenylboronate-based SERS nanoprobe for detection and imaging of intracellular peroxynitrite.

A surface-enhanced Raman scattering (SERS) based nanoprobe was developed for detection and imaging of endogenous peroxynitrite in living cells. The probe was fabricated by assembling 3-mercaptophenylboronic acid pinacol ester onto the surface of gold nanoparticles (AuNPs). The detection of peroxynitrite is accomplished via measurement of the changes in the SERS spectra (at 882 cm-1) that are caused by the reaction between probe and peroxynitrite. The probe has a fast response (<30 s), a 0.4 µM lower detection limit and a wide linearity range from 5.0 × 10-7 to 1.0 × 10-4 M. It is biocompatible and highly stable on storage and under various pH conditions. Both the reaction and the SERS signal are highly specific over other species. The nanoprobe was successfully applied to SERS imaging of peroxynitrite that is produced in macrophages under oxidative stress. Conceivably, the method has a most viable tool for use in studies on peroxynitrite-related physiological and pathological processes. Graphical abstract Schematic presentation of surface-enhanced Raman scattering (SERS) nanoprobes fabricated by assembling phenylboronate on gold nanoparticles (AuNPs) for detecting intracellular peroxynitrite (ONOO-) via specific reaction-caused SERS changes.

Reaction-based SERS nanosensor for monitoring and imaging the endogenous hypochlorous acid in living cells.

Hypochlorous acid (HOCl), as an important reactive oxygen species (ROS), is involved with many pathological and physiological pathways, whereas many aspects of its roles remain unclear due to the lack of robust analytical methods. In this work, we report a novel kind of special reaction-based nanosensors, gold nanoparticles modified with newly synthesized 2-mercapto-4-methoxy-phenol molecules (AuNPs/MMP), to detect the endogenous HOCl in living cells according to the changes in the SERS spectrum of AuNPs/MMP resulting from the reaction of HOCl with MMP on AuNPs. These nanosensors can rapidly respond to HOCl within 1 min with the detection limit at 10-7 M level. Furthermore, the nanosensors exhibit high selectivity for HOCl because of the specificity of the reaction combined with the fingerprinting capability of SERS. Consequently, the proposed SERS nanosensors are capable of monitoring and imaging the endogenous HOCl generated in a living macrophage under stimulation, showing great promise to be used for in-situ studies of the pathophysiological processes that involve HOCl.