Session: 07-05-01: Biomedical Devices, Sensors, and Actuators

Paper Number: 198894

Photothermal Recycling Biosensing for Longitudinal Biochemical Monitoring 

Biosensors that monitor circulating biomarkers have the potential to provide valuable real-time insights into the health status of patients. This is especially important for patients receiving intensive care, as their condition can change dramatically in a matter of hours or even minutes. Identifying unstable patients early and providing timely interventions is currently one of the most significant clinical challenges in intensive care. However, standard methods of diagnosis rely on clinical chemistry laboratories and time-consuming assays, making continuous monitoring and timely treatment difficult. Beyond the clinic, the same capability to track biochemical dynamics in real time is increasingly needed for bioprocess monitoring, wearable health tracking, and therapeutics.

A major technical challenge in continuous biomolecular monitoring is achieving a fast response while maintaining high specificity and sensitivity. Sensitive molecular detection requires slow analyte-binder dissociation and long incubation to reach equilibrium. Rapid sensor response, on the other hand, calls for fast analyte dissociation and association that are difficult to achieve for low-abundance analytes. This trade-off between affinity and kinetic reversibility, which we refer to as the sensitivity-speed limitation, prevents most existing affinity-based platforms from continuously measuring targets below the picomolar (pM) range, where tight binders rapidly saturate the sensing surface and lose temporal responsiveness.

To resolve this conflict, we propose a mechanism termed photothermal recycling (PTR), which mimics the thermal cycling process in the polymerase chain reaction and uses the plasmonic photothermal effect to rapidly recycle affinity reagents for frequent measurements. Instead of applying chemical, electrical, or reagent-based regeneration, PTR delivers localized thermal energy directly at the sensing surface as a universal, reagent-free driving force. Brief illumination of a plasmonic gold film generates rapid, highly localized heating that dissociates tight analyte-binder complexes, while subsequent convective cooling resets the binders for the next detection cycle with minimal delay. This allows high-affinity reagents to be reused repeatedly without saturation, decoupling sensitivity from measurement speed.

In this study, we present assay designs and optimizations that implement PTR for longitudinal biochemical monitoring. Using a DNA hairpin model on a gold surface, we first confirmed that photothermal heating reversibly modulates biomolecular recognition over repeated heating and cooling cycles. We then integrated PTR with a digital bead assay that counts individual binding events, and systematically optimized affinity, avidity, surface passivation, and illumination conditions to maximize specific binding while suppressing nonspecific fouling.

Our results demonstrate that, through molecular engineering and controlled temperature modulation, PTR enables multiple sensing cycles over several hours in complex biological matrices, including plasma, serum, and saliva. The digital PTR assay achieves sub-pM sensitivity with a dynamic range spanning about four orders of magnitude, and reliably recycles the sensing surface across at least a dozen cycles. We further show that PTR allows frequent detection of low-abundance analytes in the low-pM range using diverse binding chemistries, including DNA duplexes, aptamers, antibodies, and nanobodies. Finally, we highlight two applications: monitoring small molecules in continuous cell culture, demonstrated by inline tracking of extracellular ATP dynamics in bacterial culture, and measuring low-abundance immune mediators and hormones, demonstrated by ultrasensitive continuous detection of thrombin and cortisol in serum and saliva. Together, these results establish PTR as a versatile bioanalytical paradigm for continuous, sensitive molecular quantification across diverse settings.

Presenting Author: Jing Pan University of Florida

Presenting Author Biography: Dr. Jing Pan is an assistant professor in Mechanical and Aerospace Engineering at the University of Florida. He received his Ph.D. in Mechanical Engineering from Purdue University. During his Ph.D., Dr. Jing Pan worked on engineering DNA-based synthetic motors and optical sensors. He conducted his postdoctoral research at Stanford University where he worked on designing switchable affinity reagents for biomedical sensing applications. He currently directs the Biodesign Laboratory at UF. His research focuses on engineering biomolecules and nanomaterials for emerging biosensing applications in life science research and healthcare. He is the recipient of NIH R21 Trailblazer award and NSF CAREER award.

Authors:

Yongchen Tai University of Florida
Yida Wang University of Florida
Yunshen Li University of Florida
Wenting Wang University of Florida
Jacob Lee University of Florida
Jing Pan University of Florida