# Solvent-Driven Enrichment and Multiplex Analysis of Local Anesthetics by Thin-Layer Chromatography Coupled with Surface-Enhanced Raman Spectroscopy

## TL;DR

This paper introduces a new TLC-SERS method to detect multiple local anesthetics in human plasma with high sensitivity and efficiency.

## Contribution

A solvent-driven enrichment TLC-SERS method for sensitive and multiplex detection of six local anesthetics in plasma.

## Key findings

- The method achieved detection limits up to 2 × 10⁴ times more sensitive than previous TLC-Raman methods.
- The technique was successfully applied to human plasma samples, showing its potential for clinical and forensic use.
- Each anesthetic produced a strong and unique SERS response after Ag NPs staining.

## Abstract

Local anesthetics have been widely used in clinical analgesia due to their ability to provide effective regional pain management. Accurate measurement of local anesthetics in body fluids is crucial for ensuring patient medication safety and optimizing therapeutic efficacy. Herein, we present a convenient, economical, sensitive, and efficient TLC-SERS method for multiplex determination of six kinds of anesthetics (pro) in human plasma, including procaine hydrochloride (Pro), tetracaine hydrochloride (Tet), dibucaine (Dib), mepivacaine hydrochloride (Mep), lidocaine hydrochloride (Lid), and ropivacaine hydrochloride (Rop). The TLC method was adopted to separate six local anesthetics effectively. In order to improve the sensitivity, TLC spots were concentrated into smaller ones using methanol through solvent-driven enrichment, then Ag NPs staining was applied to enriched spots for a strong and unique SERS response of each anesthetic. As a result, linear calibration curves of SERS intensity ratio versus negative logarithm of spotting amounts sampled on TLC plates were obtained, along with the lowest detectable amounts in this study were 1 ng (Pro), 10 pg (Tet), 10 ng (Dib), 50 ng (Mep), 50 ng (Lid), and 0.1 μg (Rop), which were up to 2 × 104 times more sensitive than our previous TLC-Raman method. Moreover, the method was successfully applied to human plasma samples, demonstrating the feasibility and potential for multiplex analysis of local anesthetics in clinical practice, criminal forensics, and aquaculture.