Chemical Sensors and Specificity
Several established analytical techniques are available to identify target analytes with high certainty, e.g. various immune-based techniques, mass spectrometry or nuclear magnetic resonance. However, the equipment used for the analysis is rather costly and requieres skilled personnel to operate the system and collect data. Usually, batch sampling is performed on the spot, followed by an analysis of the samples in an analytical laboratory. This causes a considerable delay between the sampling step and the results of the analysis. However, the μMole project aims at providing an analytical tool that allows on-site continuous detection with real-time data processing and transfer of results.
We propose an analytical method based on selective recognition of the targeted compounds with miniaturized components, which will contribute to a considerable reduction in manufacture cost.
In order to manufacture such a system, our consortium works on the design and manufacturing of:
- Molecularly Imprinted Polymers (MIPs) for specific target compounds
- Multi-channel integrated low-power sampling electronic system
- Fingerprint-like pattern recognition algorithms for multi-sensor signal processing
Manufacturing of Molecularly Imprinted Polymers
We will use Molecularly Imprinted Polymers (MIPs) as recognition elements for the selected compounds of interest. These polymers act as synthetic antibodies which are characterized with a high mechanical and thermal stability, and show chemical resistance in a broad pH range and various organic and aqueous solvents. These properties make them the preferred type of receptors for application in the harsh conditions imposed by sewage systems.
An advantage of MIPs is their high affinity towards target compounds, with KD values in the range 10-5 – 10-8. On the other hand, MIPs may show elevated affinities towards other compounds as well, and therefore are characterised by low selectivity. This project aims to tackle this major problem using a multi-channel approach where channels with different MIPs perform parallel measurements. Molecular imprinting is a well-established, continuously expanding technique, whereas the multi-channel approach has been devoted less attention in literature, which indicates certain feasibility to address the problem and illustrates the novelty of this approach. Imprinted polymers towards ATS have hardly been described in literature.
Multi-channel integrated low-power sampling electronic system
The optimal combination of sensor element, chemical sensing material and readout electronics is required to develop a multichannel, low-power electro-chemical sensing subsystem for detection of synthesis impurities of synthetic drugs (e.g. Amphetamines) with a reduced probability of a false-positive alarm.
During the first project year, It was identified that the chemical sensing system needs active pumping and valves in order to fulfil these requirements. Large effort was done to select to best combination of mechanical devices and driver elements to build up a low-power system. A first prototype based on discrete components was manufactured to test the overall sensing concept and to evaluate the newly developed flow cells.
This first prototype will be utilized as a platform where project-related developments will be successively implemented and tested. The final prototype device in the Micromole project will hence be an evolutionary product of this platform. The development of the prototype reduces the design risks of the sensing sub-system and provides important data for the ASIC specification.
The Application-Specific Integrated Circuit (ASIC) development as the next step will improve the power consumption of the system and allows a significant reduction in size.
Pattern recognition for multi-sensor signal processing
Each compound present in the sewage will interact with the polymers to a different extent. The combination of several channels with different selectivity and affinity towards target compounds, will generate a pattern signal which is characteristic for this compound. All these patterns will be recorded and a pattern recognition software will be used to extract characteristic signals from the obtained data matrix.
This approach should increase the selectivity of the sensor while considering the cross-reactivity of the imprinted polymers and has several important advantages. First of all, cross-reactivity is an intrinsic property for any receptor which relies on affinity binding. A solution to circumvent this issue without the need to change the fundamental aspects of the imprinting technique is very desirable. Secondly, a comprehensive amount of literature is available concerning synthesis and applications of MIPs with affinity towards various compounds: bacteria, proteins, drugs-of-abuse, hormones, (myco-)toxins, heavy metals, etc. A multi-channel platform in which a plethora of different MIPs allows to tailor the sensor towards any desired target compounds, can benefit from a vast amount of available research. Finally, the target substances in this project are characterized with a low molecular weight and few functional groups. These are, in general, challenging compounds to detect since they often show low specificity towards (traditional) recognition elements. The compounds in this project can therefore also be considered as relevant model compounds for this large class of chemical substances.
In summary, our ambition is to create a robust and general sensing platform, which can be adapted towards the needs of the user. Choosing different imprinted polymers will allow targeting the desired compounds. The robustness intrinsic to polymers enables detection in demanding environments.
PUBLICATION1 – MICROCONTACT IMPRINTING BASED CAPACITIVE BIOSENSORS FOR REAL-TIME PROTEASE DETECTION/QUANTIFICATION -Download PDF
PUBLICATION2 – Characterisation of chemical waste from illegal amphetamine synthesis to support forensic assessment of clandestine drug laboratories – Download PDF
PUBLICATION4 – Capacitive sensing of amphetaminetype stimulants based on immobilized molecular imprinted polymers – Download DOC