Label-Free Detection of Small Organic Molecules by Molecularly Imprinted Polymer Functionalized Thermocouples: Toward In Vivo Applications

Molecularly imprinted polymers (MIPs), synthetic polymeric receptors, have been combined successfully with thermal transducers for the detection of small molecules in recent years. However, up until now they have been combined with planar electrodes which limits their use for in vivo applications. In this work, a new biosensor platform is developed by roll-coating MIP particles onto thermocouples, functionalized with polylactic acid (PLLA). As a first proof-of-principle, MIPs for the neurotransmitter dopamine were incorporated into PLLA-coated thermocouples. The response of the synthetic receptor layer to an increasing concentration of dopamine in buffer was analyzed using a homemade heat-transfer setup. Binding of the template to the MIP layer blocks the heat transport through the thermocouple, leading to less heat loss to the environment and an overall higher temperature in the measuring chamber. The measured temperature increase is correlated to the neurotransmitter concentration, which enables measurement of dopamine levels in the micromolar regime. To demonstrate the general applicability of the proposed biosensor platform, thermocouples were functionalized with similar MIPs for cortisol and serotonin, indicating a similar response and limit-of-detection. As the platform does not require planar electrodes, it can easily be integrated in, e.g., a catheter. In this way, it is an excellent fit for the current niche in the market of therapeutics and diagnostics. Moreover, the use of a biocompatible and disposable PLLA-layer further illustrates its potential for in vivo diagnostics.