# Optrode-Assisted Multiparametric Near-Infrared Spectroscopy for the Analysis of Liquids

## TL;DR

This paper introduces a new compact method using optical fibers to analyze liquids by measuring multiple properties at once.

## Contribution

A novel optrode-assisted multiparametric near-infrared spectroscopy method is introduced for liquid analysis.

## Key findings

- A broadband radiation is encoded and distributed to multiple sensing units for simultaneous interrogation.
- The setup allows spectral readout via Fourier transform of each unit's output signal.
- Simultaneous measurement of absorption spectrum and refractive index of water–methanol solutions was demonstrated.

## Abstract

We demonstrate a sensing scheme for liquid analytes that integrates multiple optical fiber sensors in a near-infrared spectrometer. With a simple optofluidic method, a broadband radiation is encoded in a time-domain interferogram and distributed to different sensing units that interrogate the sample simultaneously; the spectral readout of each unit is extracted from its output signal by a Fourier transform routine. The proposed method allows performing a multiparametric analysis of liquid samples in a compact setup where the radiation source, measurement units, and spectral readout are all integrated in a robust telecom optical fiber. An experimental validation is provided by combining a plasmonic nanostructured fiber probe and a transmission cuvette in the setup and demonstrating the simultaneous measurement of the absorption spectrum and the refractive index of water–methanol solutions.