Development of an Electrochemical Biosensor of Ubiquitin C-Terminal Hydrolase L1 (UCH-L1) for the Assessment of Traumatic Brain Injury (TBI)
Authors: Lee Jinhee , Hirano Hitomi , Tsugawa Wakako , Sode Koji 
Published: December 2020

INTRODUCTION Traumatic brain injury (TBI) is defined as a neurotrauma caused by a mechanical force applied to a head. An appropriate clinical therapy after TBI is crucial, or patients may suffer lasting effects in physical and mental abilities [1]. To find TBI, cranial computer tomography (CT) is commonly used, however, CT sometimes fails to find mild TBI (mTBI) even it accounts for majority of all cases of TBI. Recently, a blood-based biomarker, ubiquitin C-terminal hydrolase L1 (UCH-L1) has been regarded a promising marker for mTBI, as it becomes present in serum soon after TBI [2,3]. Actually, it was reported the elevated serum UCH-L1 level was observed with the soldiers exposed to low-level blast [4] and the athletes after sub-concussive dead hits [5]. Enzyme-linked immuno sorbent assay (ELISA) is currently used to detect the biomarker, however, since the ELISA is time-consuming procedure and requires specific laboratory equipment, development of a hand-held device to be used on-site in the field is expected. In this study, we propose and report a novel principle for a rapid, one-step electrochemical detection system for UCH-L1 to be dedicated for mTBI diagnosis. METHOD To detect UCH-L1, we chose an electrochemical method in terms of a rapid response time, miniaturization, and simple instrumentation. We employed a competitive assay combined with square wave voltammetry (SWV) on anti-UCH-L1 antibody immobilized electrode. In this system, a redox probe (phenazine ethosulfate: PES) modified UCH-L1 and the target biomarker is going to competitively bind to the antibody on the electrode, resulting electrochemical signal depend on the concentration of UCH-L1 in a sample. To construct the system, PES modified UCH-L1 was prepared using amine-reactive PES. This molecule has N-hydroxysuccinimide linked to PES, therefore, upon mixing amine-reactive PES with UCH-L1, it will react with amine group of lysine residue and make a covalent bond. After the modification, enzyme-linked immuno sorbent assay (ELISA) was performed to investigate the binding affinity of anti-UCH-L1 antibody against UCHH-L1 and PES modified UCH-L1. To detect UCH-L1, we added UCH-L1 together with PES-modified UCH-L1 on the antibody immobilized gold electrode, and performed SWV at a potential range of -0.5 to 0.1 V with different frequencies of square wave. RESUTLS The result of ELISA showed that the antibody had almost same affinity against non-labeled UCH-L1 and PES-modified UCH-L1. Therefore, the modification of PES did not affect the recognition of antibody. When we incubated the electrode with different concentration of PES-modified UCH-L1, a square wave voltammetry signal was increased in a concentration dependent manner, indicating the PES modified on the UCH-L1 was electrochemically active, and the amount of PES-modified UCH-L1 was detected by SWV when it was captured by anti-UCH-L1 antibody on the electrode. In the competitive assay, the incubation of intact UCH-L1 together with PES-modified UCH-L1 resulted in the SWV signal change depend on the UCH-L1 concentration. With this detection principle, we could detect UCH-L1 within 10 minutes without any washing procedure, which is ideal for the on-site detection of mTBI. CONCLUSION In this study, we developed a rapid electrochemical detection system of TBI biomarker, UCH-L1, based on the competitive of redox probe-modified UCH-L1 with the target. Using this detection system, we were able to observe SWV signal change within 10 minutes upon addition of UCH-L1. This study shows the proof-of-concept of this rapid competitive assay, and we hope it would help future development of TBI detection device. REFERENCES

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