# SERS-Based Immunoassay on Ag/ZnO Nanorod Substrates for Detection of CA125 Antigen

## TL;DR

This study develops a SERS-based immunoassay using Ag/ZnO nanorods to detect the CA125 cancer biomarker without a Raman reporter.

## Contribution

A novel Ag/ZnO nanorod substrate is introduced for SERS detection of CA125 with performance comparable to ELISA.

## Key findings

- CA125 was detected in the range of 15–1000 U/mL using the Ag/ZnO NR substrate.
- A Raman vibration mode at 829 cm–1 showed excellent linearity with CA125 concentration.
- The limit of detection was estimated at 14 U/mL.

## Abstract

Several reports have
been published on the detection of the carbohydrate
antigen 125 (CA125) cancer biomarker, where the immunoassay is completed
with a molecule tag that is detected via surface-enhanced Raman scattering
(SERS); however, it is still challenging to detect protein biomarkers
without a Raman reporter. In this study, a SERS substrate based on
zinc oxide nanorods (ZnO NRs) decorated with silver nanoparticles
was fabricated, functionalized, and bioconjugated to detect CA125.
Functionalization was performed by using an MPA self-assembled monolayer,
which was subsequently surface-activated with an EDC/NHS solution.
This process was optimized by using Raman measurements to determine
the surface protonation of the substrate. The effect of the concentration
and incubation time of the CA125 antibodies on the bioconjugation
of the substrate were evaluated. SERS detection of CA125 was successfully
achieved in a concentration range of 15–1000 U/mL, demonstrating
performance comparable to the ELISA approach. A vibration mode at
829 cm–1 associated with proline and tyrosine was
identified and exhibited excellent linearity with CA125 concentration.
A limit of detection (LoD) of 14 U/mL was estimated. This report confirms
the potential of Ag/ZnO NR substrates for developing SERS assays for
tumor marker detection using a portable Raman spectrometer.