In this work, we will present a novel approach for the detection of small molecules with molecularly imprinted polymer (MIP)-type receptors. This heat-transfer method (HTM) is based on the change in heat-transfer resistance imposed upon binding of target molecules to the MIP nanocavities. Simultaneously with that technique, the impedance is measured to validate the results. For proof-of-principle purposes, aluminum electrodes are functionalized with MIP particles, and L-nicotine measurements are performed in phosphate-buffered saline solutions. To determine if this could be extended to other templates, histamine and serotonin samples in buffer solutions are also studied. The developed sensor platform is proven to be specific for a variety of target molecules, which is in agreement with impedance spectroscopy reference tests. In addition, detection limits in the nanomolar range could be achieved, which is well within the physiologically relevant concentration regime. These limits are comparable to impedance spectroscopy, which is considered one of the state-of-the-art techniques for the analysis of small molecules with MIPs. As a first demonstration of the applicability in biological samples, measurements are performed on saliva samples spiked with L-nicotine. In summary, the combination of MIPs with HTM as a novel readout technique enables fast and low-cost measurements in buffer solutions with the possibility of extending to biological samples.

Abstract:In previous work, the novel heat-transfer method (HTM) for the detection of small molecules with Molecularly Imprinted Polymers (MIP)-type receptors was presented. In this study we focus on optimization of this sensor performance, with as final aim to lower the detection limit by reducing the noise level. It was determined that the noise originates foremost from the power supply, which can be controlled by varying the PID parameters. Therefore, the effect of the individual parameters was evaluated by tuning P, I and D separately at a temperature of 37 °C, giving a first indication of the optimal configuration. Next, a temperature profile was programmed and the standard deviation of the heat-transfer resistance over the entire regime was studied for a set of parameters. The optimal configuration, P1-I6-D0, reduced the noise level with nearly a factor of three compared to the original parameters of P10-I5-D0. With the optimized settings, the detection of L-nicotine in buffer solutions was studied and the detection limit improved significantly from 100 nM to 35 nM. Summarizing, optimization of the PID parameters and thereby improving the detection limit is a key parameter for first applications of the HTM-method for MIP receptors in analytical research.

In this article, we report on the label-free real-time thermal monitoring of the denaturation of specific DNA fragments and its potential to detect and quantify single nucleotide polymorphisms (SNPs). Probe DNA, consisting of a 36-mer fragment was covalently immobilized on nanocrystalline chemical vapour deposition (CVD) diamond platforms and hybridized with a 29-mer target DNA fragment (full matching and/or with a point mutation). It was observed that the change in heat transfer resistance upon denaturation is dependent on the amount of DNA hybridized to the nanocrystalline diamond (NCD) surface. Furthermore the possibility to distinguish between a full matching sequence and its singularly mutated counterpart, when bound to the same NCD surface, was investigated. NCD surfaces were selectively hybridized with both full matching and mutated DNA fragments at different ratios (3:1, 2:2 and 1:3). A clear bipartite response in heat transfer resistivity was observed upon simultaneous denaturation of these DNA fragments. Denaturation temperature could be used to identify the DNA fragment to which each partial response could be attributed. Moreover, the partial increases in heat transfer resistivity related to the hybridized amount of non-mutated or mutated DNA, respectively. These results imply that heat transfer resistivity is a technique which can be used to (i) quantify DNA fragments of interest, (ii) detect and (iii) quantify SNPs in a mixture of mutated and non-mutated DNA fragments. Moreover, it illustrates the potential of this technique to detect SNPs without the necessity to design complex microarrays.