A portable platform for renal function monitoring: simultaneous quantification of creatinine and uric acid using a smartphone-coupled photonic crystal sensor

Given the intricate pathophysiological interplay between renal dysfunction and metabolic disorders, the multiplexed detection of creatinine and uric acid is indispensable for the holistic risk stratification and management of chronic kidney disease (CKD). To tackle poor signal-to-noise ratios at trace analyte concentrations, we developed a photonic crystal (PC)-based sensing chip for the simultaneous detection of creatinine and uric acid, utilizing NaYF₄:Yb,Er@NaYF₄ and NaErF₄:Tm@NaYF₄ upconversion nanoprobes. Notably, the integration of the PC led to a 5.9-fold and 3.8-fold enhancement in the detection sensitivity for creatinine and uric acid, respectively. This improvement is attributed to the efficient signal amplification derived from the Bragg mirror reflection effect inherent to the PC structure. The chip exhibited excellent stability and accuracy in complex biological matrices, including serum and whole blood, with relative deviations from clinical standards of less than 4.1% and 2.0%, respectively. By integrating the chip with a smartphone application, we established a portable analysis system that automatically captures and processes fluorescence images to provide visual, quantitative readouts. This work proposes a generic strategy for amplifying fluorescence-based biosensing technology, offering a powerful tool for the rapid, low-cost diagnosis of CKD and paving the way for next-generation high-performance point-of-care testing platforms.