口腔癌的早期诊断，需要高特异性和敏感性的口腔肿瘤标志物现场检测，但由于口腔液中这些生物标志物的浓度较低，因此仍然具有挑战性。因此，本文提出了一种基于光子晶体（OPC）增强上转换荧光的熄灭型生物传感器，采用荧光共振能量转移感应策略，在唾液中检测癌胚抗原（CEA）。通过在上转换纳米颗粒上修饰亲水性PEI配体，以促进唾液与检测区域的充分接触，增强生物传感器的灵敏度。作为生物传感器的底物，OPC还可通过结合停止带和激发光来提供局部场效应，从而显着增强上转换荧光，获得66倍的放大倍数。对于唾液中的CEA检测，此类传感器在0.1-2.5 ng/mL和大于2.5 ng/mL的范围内都表现出良好的线性关系，检测限降至0.1 ng/mL。此外，通过监测真实唾液，确认了患者与健康人之间的有效差异，表明在临床早期诊断和家庭自我监测肿瘤方面具有重要的实用价值。Copyright © 2023 Elsevier B.V. All rights reserved.

The point-of-care test of tumor markers in saliva with high specificity and sensitivity for early diagnosis of oral cancer is of great interest and significance, but remaining a daunting challenge due to the low concentration of such biomarkers in oral fluid. Herein, a turn-off biosensor based on opal photonic crystal (OPC) enhanced upconversion fluorescence is proposed to detect the carcinoembryonic antigen (CEA) in saliva by applying fluorescence resonance energy transfer sensing strategy. Hydrophilic PEI ligands are modified on upconversion nanoparticles to enhance the sensitivity of biosensor by promoting sufficient contact between saliva and detection region. As a substrate for the biosensor, OPC can also provide a local-field effect for greatly enhanced upconversion fluorescence by coupling the stop band and excitation light, and a 66-fold amplification of the upconversion fluorescence signal was obtained. For the CEA detection in spiked saliva, such sensors showed a favorable linear relationship at 0.1-2.5 ng mL-1 and more than 2.5 ng mL-1, respectively. The limit of detection was down to 0.1 ng mL-1. Moreover, by monitoring real saliva, the effective discrepancy between patients and healthy people was confirmed, indicating remarkable practical application value in clinical early diagnosis and home-based self-monitoring of tumors.Copyright © 2023 Elsevier B.V. All rights reserved.