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

Abstract

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.

A novel thermal detection method based on molecularly imprinted nanoparticles as recognition elements

“…In previous work, 27 the authors described polylactic acid (PLLA) coated thermocouples that were impregnated with MIP particles. The PLLA-sheet (∼2 μm thickness) forms a thermally insulating layer around the thermocouple over the entire sheet within the flow cell.…”

“…With the dose-response curve and obtained fit, a LoD value of 3 ± 1 nM in PBS was estimated, which was an improvement of nearly three orders of magnitude compared to previous works on thermocouples. 27 The explanation behind this is threefold; first, there is a ten-fold decrease in layer thickness that promotes heat-flow through the surface and increases the response to changes in the thermal signal and, second, the increased surface-to-volume ratio of the nanoparticles and, third, the higher affinity of the nanoMIPs towards its template. It is also an improvement compared to the more conventional approach where MIP particles were functionalised onto an electrode surface rather than directly on the thermocouple, which attained LoDs between 25-100 nM for small molecules in buffered solutions.…”

“…A straightforward approach is to directly deposit MIP particles onto thermocouples that are used for the determination of the temperature in the liquid. 27 While this simplifies data analysis, it requires the use of additional layers to attach the MIP layers on the thermocouples. In addition, the microparticles hinders heat-flow through the thermocouple, thereby rendering detection less efficient and increasing the noise on the signal.…”

Studying the Effect of Adhesive Layer Composition on MIP‐Based Thermal Biosensing

“…MIP particles for small molecules are often made in an external reaction vessel and need to be deposited onto the planar measurement electrode using an immobilization layer made by, e.g., spin coating or dip coating. In the latter case, it was recently demonstrated that it is possible to dip coat thermocouples with DNA and roll coat them with polymeric particles for the direct detection of molecules in aqueous media without the need of planar electrodes . Although, this approach is promising, the smaller contact area of the thermocouple limits the sensitivity of the methodology.…”

Single-Shot Detection of Neurotransmitters in Whole-Blood Samples by Means of the Heat-Transfer Method in Combination with Synthetic Receptors

“…When template molecules bind to the MIP receptor layer, the thermal resistance increases and detection of serotonin in buffer solutions in the low nanomolar regime was demonstrated [ 21 ]. The thermal readout platform could be combined with various other receptors leading to other biosensing applications, such as DNA mutation analysis, phase changes in lipids, and detection of cells, but biological samples remained to be evaluated [ 26 , 27 , 28 ].…”