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To meet the increasing need for point-of-care testing (POCT), simple and portable readout strategies would be highly desirable. Thermometer with high accuracy and straightforward readout is an ideal tool for the development of new POCT methods. The exploration of new thermometer-based detection methods is of great significance. In this study, a simple biosensor for glucose based on the photothermal effect of gold nanorods using a simple thermometer as readout has been developed. In the presence of glucose oxidase, glucose can react with the dissolved oxygen to produce H 2 O 2. With the help of Fe2+, H 2 O 2 can etch gold nanorods (AuNRs) to different aspect ratios. The decrease of the aspect ratio of AuNRs leads to the blue-shift of the localized surface plasmon resonance peak, resulting in a decrease of photothermal effect in the near-infrared regions and the temperature of the system decreased. The change of the temperature has a linear relationship with the logarithm of glucose concentration in the range of 1.0–10.0 mM with a detection limit of 0.8 mM. The proposed method possesses a bias offset of −0.03 mM for glucose detection compared to the hospital method. Since many enzymatic reactions can produce H 2 O 2 , the principle can be modified to detect different targets by simply change of the enzyme used. A photothermal biosensor for glucose based on the different photothermal effect of different aspect ratio of gold nanorods has been developed. [Display omitted] • Etching of gold nanorods effectively decrease their photothermal effect. • Molecular detection was translated into a simple temperature test. • This mechanism can be adjusted to detect other targets by changing the enzyme. [ABSTRACT FROM AUTHOR]