Design and Optimization of a Highly Sensitive Surface Plasmon Resonance Biosensor for Accurate Detection of Mycobacterium tuberculosis
Tuberculosis (TB) continues to be a critical global health issue, with 10.6 million cases and over 1.3 million deaths in 2022. The World Health Organization (WHO) aims to eliminate the TB epidemic by 2030. To achieve this, rapid and accurate diagnosis, especially in low-resource settings, is essential. Traditional diagnostics, such as culture or smear microscopy, are either too slow or not sufficiently sensitive. The work presents a highly sensitive, compact, and practical Surface Plasmon Resonance (SPR) biosensor for the detection of Mycobacterium tuberculosis with exceptional performance metrics.
The sensor is based on a seven-layer hybrid configuration: N-FK51A prism/titanium dioxide (TiO₂)/silicon (Si)/silver (Ag)/barium titanate (BaTiO₃)/Black Phosphorus (BP). This structure was optimized through theoretical modeling and simulation (Transfer Matrix Method and Finite Element Method), showing a peak angular sensitivity of 540.67 degrees/RIU, minimum full-width at half-maximum (FWHM) of 3.6740, detection accuracy (DA) of 0.27, signal-to-noise ratio (SNR) of 1.031, and an outstanding quality factor (QF) of 133.30 RIU⁻¹.
This work demonstrated that material choice and precise thickness tuning are critical. A 45 nm Ag layer provided the best balance between plasmonic enhancement and structural stability. Similarly, 5 nm Si and 7.52 nm BaTiO₃ yielded optimal interaction conditions for enhanced field confinement. A BP layer of just 0.53 nm, due to its high carrier mobility and tunable bandgap, significantly boosted environmental responsiveness and sensor sensitivity. The researchers also confirmed that N-FK51A is the optimal prism material compared to BK7 or SF5, achieving the highest angular shift for TB markers.
To ensure practical deployment, a scalable fabrication process was proposed using common techniques such as radio frequency (RF) sputtering, atomic layer deposition (ALD), plasma-enhanced chemical vapor deposition (PECVD), and chemical vapor deposition (CVD). The experimental setup includes a He–Ne laser (633 nm), a microfluidic flow cell, and controlled injection of ligand and analyte. The microfluidic design maintains refractive index (RI) stability and bio sample integrity. The reflectivity changes due to the presence of biomarkers were recorded and visualized, confirming the system’s reliability.
A key finding of the study was the impact of penetration depth (PD) of the evanescent field. At an incident angle of 86.8° (RI = 1.351), the PD reached ~180 nm, sufficient for biomarker-level interactions, before the field decayed to 1/e of its maximum intensity. The researchers thoroughly analyzed how this depth changes with varying material thicknesses, revealing a strong correlation between layer precision and sensing efficiency.
In comparison with other 2D materials (graphene, MoS₂, MXene), BP consistently outperformed in all TB sample cases (TB1–TB4). The proposed biosensor’s superior sensitivity, rapid response, and compatibility with biological refractive index ranges (1.29–1.35) make it an excellent candidate for point-of-care TB diagnostics. It can potentially be extended to detect other pathogens or even cancer markers by tuning layer properties.
This SPR biosensor bridges the gap between academic innovation and real-world usability, which can improve the efficiency of TB diagnosis and its effective treatment, and pave the way for future integrated biosensing systems.