# Cost-Effective and High-Throughput WSPRi Sensing System Based on Multi-Monochromatic LEDs and Adaptive Second-Order Fitting Algorithm

## TL;DR

A low-cost, high-throughput SPRi system using LEDs and an adaptive algorithm enables real-time biochemical sensing and early osteoarthritis detection.

## Contribution

A cost-effective SPRi system using multi-LEDs and an adaptive second-order fitting algorithm for rapid and accurate resonance wavelength reconstruction.

## Key findings

- The system achieves a scanning cycle of 105 ms and RI resolution of 5.54 × 10−6 RIU.
- It successfully monitored antibody–antigen interactions and detected COMP in synovial fluid.
- The system showed elevated COMP concentration in osteoarthritis samples compared to controls.

## Abstract

Surface Plasmon Resonance imaging (SPRi) is a powerful label-free technique for high-throughput biochemical analysis. Wavelength modulation is particularly suitable for SPRi due to its wide dynamic range and robustness to fabrication tolerances. However, conventional systems relying on tunable filters (e.g., AOTF, LCTF) suffer from high cost, complexity, and limited temporal resolution. To overcome these drawbacks, we developed a rapid wavelength-modulation SPRi system using a multi-LED source and an adaptive second-order fitting (ASF) algorithm. The system covers the 730–805 nm spectrum with five LEDs. The ASF algorithm first performs a coarse full-spectrum scan to locate the resonance wavelength, then dynamically selects an optimal three-LED subset for fast second-order fitting, enabling accurate reconstruction of resonance wavelength without mechanical scanning. This approach significantly reduces cost and complexity while achieving a scanning cycle of 105 ms, RI resolution of 5.54 × 10−6 RIU, dynamic range of 0.0241 RIU, and excellent multi-channel consistency. The system has been successfully applied to monitor multi-channel antibody–antigen interactions in real time. Furthermore, it was used to detect cartilage oligomeric matrix protein (COMP) in synovial fluid, where an elevated concentration in an osteoarthritis sample versus a control aligned with its role as a cartilage catabolism marker. This work validates a practical and reliable platform for early diagnosis of osteoarthritis.