Double Stopband Bilayer Photonic Crystal Based Upconversion Fluorescence PSA Sensor

Precise detection on tumor markers is significant for the early diagnosis on cancer. Upconversion fluorescence probes are ideal for tumor marker sensing, but still subject to bottleneck problems of low emission efficiency/strength. In this work, a novel bilayer of poly(methyl methacrylate) opal photonic crystal (PMMA OPC) with double photonic stop bands was fabricated to match the excitation field and emission field of the upconversion nanoparticles (UCNPs) at the same time, and greatly enhance their upconversion fluorescence intensity. Herein, NaYF4:Yb3+,Er3+ UCNPs and NaYF4:Yb3+,Er3+@NaYF4:Yb3+,Nd3+ UCNPs with a core-shell structure were employed as a core, which could be excited by 980 nm and 808 nm light, respectively. With the optimized geometry structure, the upconversion emission intensity was enhanced over 150 folds under the excitation of both 808 nm and 980 nm laser. Through the NaYF4/OPC biochip and florescence resonant energy transfer (FRET) sensing strategy, the lowest detection limit of 0.01 ng/mL with good linear relationship was obtained ranging from 0.1 ng/mL to 10 ng/mL. The power density of the pumping light was as low as 1.7 W/cm2. This enhanced upconversion tumor marker biochip sensor provides a promising and powerful tool for facile early diagnosis on cancer markers.