Continuous and in situ detection of biomarkers in biofluids (for example, sweat) can provide critical health data but is limited by biofluid accessibility. Here we report a sensor design that enables in situ detection of solid-state biomarkers ubiquitously present on human skin. We deploy an ionic–electronic bilayer hydrogel to facilitate the sequential dissolution, diffusion and electrochemical reaction of solid-state analytes. We demonstrate continuous monitoring of water-soluble analytes (for example, solid lactate) and water-insoluble analytes (for example, solid cholesterol) with ultralow detection limits of 0.51 and 0.26 nmol cm⁻², respectively. Additionally, the bilayer hydrogel electrochemical interface reduces motion artefacts by a factor of three compared with conventional liquid-sensing electrochemical interfaces. In a clinical study, solid-state epidermal biomarkers measured by our stretchable wearable sensors showed a high correlation with biomarkers in human blood and dynamically correlated with physiological activities. These results present routes to universal platforms for biomarker monitoring without the need for biofluid acquisition.

生物体液（例如汗液）中生物标志物的连续原位检测可以提供关键的健康数据，但受到生物体液可及性的限制。在这里，我们报告了一种传感器设计，可以原位检测人体皮肤上普遍存在的固态生物标志物。我们采用离子-电子双层水凝胶来促进固态分析物的连续溶解、扩散和电化学反应。我们展示了对水溶性分析物（例如固体乳酸）和水不溶性分析物（例如固体胆固醇）的连续监测，检测限分别为 0.51 和 0.26 nmol cm ⁻² 超低。此外，与传统的液体传感电化学接口相比，双层水凝胶电化学接口将运动伪影减少了三倍。在一项临床研究中，通过我们的可拉伸可穿戴传感器测量的固态表皮生物标志物显示出与人体血液中的生物标志物高度相关，并且与生理活动动态相关。这些结果为无需采集生物体液的生物标志物监测通用平台提供了途径。