Thermistors coated with molecularly imprinted nanoparticles for the electrical detection of peptides and proteins.

In this communication, molecularly imprinted nanoparticles (nanoMIPs) that are produced by solid-phase synthesis are functionalised onto thermistors via dip-coating. These thermistors are soldered onto a printed-circuit board to facilitate electrical detection. Subsequently, these are inserted into a home-made thermal device that can measure the selective binding of biomolecules to the nanoMIP layer via monitoring the thermal resistance (Rth) at the solid-liquid interface. This thermal analysis technique, referred to as the Heat-Transfer Method, has previously been used for detection of proteins with MIP-based binders. While offering the advantages of low-cost and label free analysis, this method is limited by the high noise on the feedback loop and not being commercially available. These disadvantages can be overcome by the use of thermistors, which offer superior temperature sensitivity compared to thermocouples, and its electrical read-out can be easily integrated into portable devices. To our knowledge, this is the first report where MIPs are directly integrated onto thermistors for detection purposes. Measurements were conducted with an epitope of epidermal growth factor receptor (EGFR) and trypsin, where the electrical resistance was correlated to the biomolecule concentration. For both EGFR and trypsin, an enhanced signal to noise ratio for the electrical measurements was observed compared to previous analysis that was based on thermal resistance. The sensitivity of the sensors in buffered solution was in the nanomolar range, which is compatible with physiologically relevant concentrations. Upon exposure of the nanoMIP for EGFR towards pepsin no significant change in the resistance was yielded, establishing the selectivity of the developed sensor platform. Besides the enhanced sensitivity, the use of thermistors will enable miniaturisation of the device and has potential for in vivo measurements since specified electrochemical measurements are compatible with human use. To highlight the versatility of the nanoMIPs, this work should be extended to a set of biomolecules with various structures, with the possibility of extending this to an array format.

Evaluating the potential of thermal read-out techniques combined with molecularly imprinted polymers for the sensing of low-weight organic molecules.

In recent years, there has been a tremendous increase in the papers published on synthetic recognition elements. Molecularly imprinted polymers (MIPs), also referred to as "man-made mimics" of antibodies, are able to rebind their template molecules with high affinity. Advantages compared with those of natural receptors include their excellent thermal and chemical stability, low cost, and ease of the production process. However, their use in commercial biosensors is limited owing to the difficulty to incorporate MIPs into suitable sensing platforms and traditional detection techniques, such as chromatography, that require bulky and sophisticated equipment. In this review, we evaluate the potential to use MIPs combined with thermal read-out for the detection of low-weight organic molecules. We discuss thermal methods to study MIP-template complexation and to determine neurotransmitters concentrations. In particular, we highlight the heat-transfer method, a recent technique that is straightforward and low cost and requires minimal instrumentation. Until now, sample preparation involves a 2-step process, making it time-consuming, and measuring biological samples is difficult owing to the noise in the signal. Different sample preparation methods are discussed, and it will be demonstrated how this affects the thermal response. An outlook is given in novel methods that can simplify and speed up sample preparation. Finally, we show a novel thermal technique, which is based on the analysis of transport of thermal waves rather than evaluating the fixed heat-transfer resistance. Through applying the concept of thermal waves, signal-noise ratio is significantly increased, which results in lower detection limits and has potential for the study of biological samples.

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

Molecularly Imprinted Polymers (MIPs) are synthetic receptors that are able to selectively bind their target molecule and, for this reason, they are currently employed as recognition elements in sensors. In this work, MIP nanoparticles (nanoMIPs) are produced by solid-phase synthesis for a range of templates with different sizes, including a small molecule (biotin), two peptides (one derived from the epithelial growth factor receptor and vancomycin) and a protein (trypsin). NanoMIPs are then dipcoated on the surface of thermocouples that measure the temperature inside a liquid flow cell. Binding of the template to the MIP layer on the sensitive area of the thermocouple tip blocks the heat-flow from the sensor to the liquid, thereby lowering the overall temperature measured by the thermocouple. This is subsequently correlated to the concentration of the template, enabling measurement of target molecules in the low nanomolar regime. The significant improvement in the limit of detection (a magnitude of three orders compared to previously used MIP microparticles) can be attributed to their high affinity, enhanced conductivity and increased surface-to-volume ratio. It is the first time that these nanosized recognition elements are used in combination with thermal detection, and it is the first report on MIP-based thermal sensors for determining protein levels. The developed thermal sensors have a high selectivity, fast measurement time (<5 min), and data analysis is straightforward, which makes it possible to monitor biomolecules in real-time. The set of biomolecules discussed in this manuscript show that it is possible to cover a range of template molecules regardless of their size, demonstrating the general applicability of the biosensor platform. In addition, with its high commercial potential and biocompatibility of the MIP receptor layer, this is an important step towards sensing assays for diagnostic applications that can be used in vivo.