Sensor Science

Faculty currently associated with this research theme.

Implantable, Anti-Fouling Biomedical Sensors +

Accurate monitoring of glucose and lactate levels in blood is of great biomedical importance in the critical care setting. The ability to monitor these and related compounds continuously via an intravenous catheter at the patient’s bedside would provide a means to assess whether prescribed clinical therapies are working to save the patient.  Work in the Meyerhoff group has shown that polymers capable of releasing 1–15×10−10 mol min−1 cm−2 of NO at the polymer/blood interface can effectively decrease the platelet adhesion and thrombus formation on the surfaces of implanted devices. Further, electrochemical glucose sensors prepared with NO releasing outer polymeric membranes greatly decrease the in vivo inflammatory response during the initial subcutaneous implantation in rats (when compared to control sensors implanted in the same animals), without degrading the analytical performance of the sensor itself. Recent work has made use of a newly formulated NO release coating that consists of a lipophilic diazeniumdiolate species (N-diazeniumdiolated dibutylhexanediamine, DBHD/N2O2) embedded within a layer of poly(lactide-co-glycolide) (PLGA), which is then covered by a outer layer of PurSil (polyurethane/dimethylsiloxane copolymer). DBHD/N2O2 readily releases NO upon contact with water by a proton driven mechanism. The use of PLGA as a matrix for the diazeniumdiolate NO donor provides an added source of protons to promote extended NO release, without the need for using tetraphenylborate derivative additives.

Micro-GC for On-Site Detection/Analysis +

Work in the Zellers group has demonstrated, for the first time, a fully integrated, fieldable, gas chromatographic microanalytical system (µGC) for near-real-time determinations of trace-level vapor concentrations of marker compounds of explosives. A top view of the current field prototype is shown above. It uses an adsorbent-packed, deep-reactive-ion-etched (DRIE) Si/glass microfocuser, a wall-coated DRIE-Si/glass microcolumn, and an integrated array of 4 chemiresistors coated with functionalized thiolate-monolayer-protected gold nanoparticle (MPN) interface layers. A high-volume sampler is connected upstream to reduce analysis time and detection limits. Commercial valves and mini-pumps are used. All functions are set and automatically sequenced by a laptop computer, which runs routines written in-house in LabView. Laboratory testing of the field prototype was performed with the following explosive markers: 2,4-dinitrotoluene (2,4-DNT) and 2,3-dimethyl-2,3-dinitrobutane (DMNB, an explosive taggant). Calculated limits of detection are 2.2 and 0.85 ng, corresponding to 0.31 and 0.11 ppb, for DMNB and 2,4-DNT, respectively (1-L sample). In the analysis of the mixture of the two markers 19 other compounds, all components are completely resolved from the target analytes and a complete analysis requires just 2.7 min.

Advanced Sampling Methods for In-Vivo Chemical Monitoring +

Developing sensors for in vivo chemical monitoring is a daunting challenge. An alternative approach is to couple sampling methods with online analytical techniques; however, such approaches are generally hampered by lower temporal resolution and slow analysis. Recent work in the Kennedy group coupled microdialysis sampling with segmented flow electrospray ionization mass spectrometry (ESI-MS) to perform in vivo chemical monitoring. The use of segmented flow to prevent Taylor dispersion of collected zones and rapid analysis with direct ESI-MS allowed 5 s temporal resolution to be achieved. The MS “sensor” was applied to monitor acetylcholine in the brain of live rats. The detection limit of 5 nM was sufficient to monitor basal acetylcholine as well as dynamic changes elicited by microinjection of neostigmine, an inhibitor of acetycholinesterase, that evoked rapid increases in acetycholine and tetrodotoxin, a blocker of Na+ channels, that lowered the acetylcholine concentration. Related sampling techniques like push-pull perfusion coupled with ESI-MS provide powerful in vivo detection strategies with good temporal resolution and selectivity.

Sensing via Analyte-triggered Gel Formation +

Chemical and biological sensors can range in complexity from state-of-the-art instrumentation to disposable test strips. Although many analytes have existing detection systems, each new environment demands a unique solution. Moreover, sensors that have a rapid response rate and are inexpensive, portable, and disposable are lacking for many analytes. Work in the McNeil group is aimed at developing simple, low-cost indicators and diagnostic devices using analyte-induced solution-to-gel phase transitions. The principle advantages of these responsive gel-based materials are that the yes/no signal is unambiguously detected by sight and the analyte concentration can be determined from the rate of gelation. Designing gelators is challenging because many factors can influence their self-assembly, including molecular structure and medium effects. One strategy is for the analyte to react with a precursor, introducing some attractive 1D intermolecular interactions that then promote gel formation.