# Integrated collinear refractive index sensor with Ge PIN photodiodes

## TL;DR

This paper introduces a CMOS-compatible refractive index sensor integrating a Ge PIN photodiode with a plasmonic nanohole array, enabling sensitive, label-free detection of molecular binding events on-chip without external instrumentation.

## Contribution

It presents a novel on-chip biosensor combining plasmonic nanostructures with a Ge PIN diode for direct, sensitive refractive index measurement in a CMOS-compatible platform.

## Key findings

- Sensitivity > 1000 nm per refractive index unit
- Operates with simple top illumination
- No external signal amplification needed

## Abstract

Refractive index sensing is a highly sensitive and label-free detection method for molecular binding events. Commercial implementations of biosensing concepts based on plasmon resonances typically require significant external instrumentation such as microscopes and spectrometers. Few concepts exist that are based on direct integration of plasmonic nanostructures with optoelectronic devices for on-chip integration. Here, we present a CMOS-compatible refractive index sensor consisting of a Ge heterostructure PIN diode in combination with a plasmonic nanohole array structured directly into the diode Al contact metallization. In our devices, the photocurrent can be used to detect surface refractive index changes under simple top illumination and without the aid of signal amplification circuitry. Our devices exhibit large sensitivities > 1000 nm per refractive index unit in bulk refractive index sensing and could serve as prototypes to leverage the cost-effectiveness of the CMOS platform for ultra-compact, low-cost biosensors.

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Source: https://tomesphere.com/paper/1902.01074