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.
The need for more advanced, accurate and lower cost sensor platforms is constantly growing. However, for certain applications the already existing sensing systems based on biological recognition elements have sometimes restrictions, which limit their use. As a result, sensors with synthetic recognition elements, such as molecular imprinted polymers (MIPs), can be interesting alternatives. Molecular imprinting leads to the formation of inert polymer particles with nanocavities, which can exhibit similar selectivity and specificity to target molecules as antibodies or enzymes. It is demonstrated that MIPs can be readily incorporated into two different sensor platforms for the detection of histamine in aqueous media. The first platform is based on electrochemical impedance spectroscopy and allows for the accurate detection of histamine in the nanomolar range. The second sensing technique is based on microgravimetry and allows for the detection of histamine in the micromolar range. Using the analogous molecule histidine, it is demonstrated that both sensor platforms are specific for the detection of histamine.
Molecularly imprinted polymers (MIPs) are synthetic receptors that are able to specifically bind their target molecules in complex samples, making them a versatile tool in biosensor technology. The combination of MIPs as a recognition element with quartz crystal microbalances (QCM-D with dissipation monitoring) gives a straightforward and sensitive device, which can simultaneously measure frequency and dissipation changes. In this work, bulk-polymerized L-nicotine MIPs were used to test the feasibility of L-nicotine detection in saliva and urine samples. First, L-nicotine-spiked saliva and urine were measured after dilution in demineralized water and 0.1× phosphate-buffered saline solution for proof-of-concept purposes. L-nicotine could indeed be detected specifically in the biologically relevant micromolar concentration range. After successfully testing on spiked samples, saliva was analyzed, which was collected during chewing of either nicotine tablets with different concentrations or of smokeless tobacco. The MIPs in combination with QCM-D were able to distinguish clearly between these samples: This proves the functioning of the concept with saliva, which mediates the oral uptake of nicotine as an alternative to the consumption of cigarettes.
Molecularly imprinted polymers (MIPs) offer a huge potential in the development of cheap small-scale disposable biomimetic sensors. They are suited for a wide variety of biological targets and are compatible with many different measurement techniques such as gravimetric sensing and impedance spectroscopy. One potential sensor platform for MIP-based biosensors is the quartz crystal microbalance (QCM). A 4-channel MIP/nonimprinted polymer (NIP) coated QCM biosensor array was developed on a single piece of quartz crystal. To study cross-channel frequency coupling of the resonance modes, a simulation of crystal designs using finite element analysis (FEA) modeling was created. Based on these simulations and using reactive ion etching (RIE) to create mesa-like structures on the crystal surface, crosstalk can be severely reduced. The improved functionality compared to the traditional QCMs was demonstrated by employing these mesa-type multichannel QCM (MQCM) crystals as an L-nicotine biosensor platform.
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