# A dynamically tunable terahertz human serum albumin biosensor based on Dirac semimetal nanozyme

## TL;DR

This paper introduces a tunable terahertz biosensor using a Dirac semimetal to detect human serum albumin with high sensitivity and potential for real-time monitoring in medical applications.

## Contribution

The novelty lies in the integration of a Dirac semimetal with a photonic crystal to create a dynamically tunable, highly sensitive biosensor for label-free HSA detection.

## Key findings

- The biosensor achieves a reflection dip deeper than 99% near 1 THz with high angular sensitivity.
- The sensor's sensitivity can be dynamically adjusted by tuning the Fermi level of the Dirac semimetal.
- The platform shows potential for real-time monitoring of nanoenzyme catalytic efficiency due to its field enhancement and tunability.

## Abstract

This study presents a tunable terahertz biosensor based on a hybrid architecture integrating bulk Dirac semimetal (BDS) with a photonic crystal for the label-free and highly sensitive detection of human serum albumin (HSA). The sensor exhibits a sharp Fano resonance resulting from the synergistic coupling between a defect mode and the BDS-mediated plasmonic response, with its resonance frequency being highly sensitive to variations in the refractive index of the sensing layer. Electric field simulations confirm significant field confinement and enhancement within the sensing region. The electrically tunable property of BDS allows dynamic reconfiguration of the sensor’s sensitivity by adjusting the Fermi level (0.1–0.4 eV), though at the expense of a reduced figure of merit (FOM) due to broader resonance peaks and increased loss, necessitating a balance in practical implementations. Structural parameter analysis reveals that sensitivity is inversely proportional to the sensing layer thickness and gradually decreases with increasing refractive index. The proposed biosensor achieves a reflection dip deeper than 99% near 1 THz, with an angular sensitivity of 247.5°/RIU for minute refractive index changes (Δn = 0.002), demonstrating high sensitivity and excellent electrical tunability. This platform demonstrates pioneering potential in integrating diagnostic-treatment nanotechnology. Due to the powerful local field enhancement generated by the BDS photonic crystal heterostructure, the imaging sensitivity of the contrast agent based on nanoenzymes has been significantly improved. Moreover, the profound local field enhancement and dynamic tunability of this platform suggest its potential for real-time monitoring and regulation of the catalytic efficiency of nanoenzymes, which could address a fundamental challenge in therapeutic applications. Combined with its inherent biocompatibility and strong detection capabilities, this framework proposes a viable pathway toward the clinical translation of nanoenzyme technology. Our work thus establishes a foundational platform that paves the way for future multifunctional theranostic systems capable of combining sensitive biomarker monitoring with enhanced therapeutic effects.