Dr Patrick Sears is a Senior Lecturer of Chemistry and Forensic analysis at the University of Surrey in the School of Chemistry and Chemical Engineering. His research expertise and background include developing analytical chemistry solutions for complex problems and understanding how analytical systems can be broken down to improve precision and accuracy. Dr Sears received his B.Sc. (1995) and M.Sc. (1996) from the University of Durham before completing a Ph.D. at the University of Hull completing research on the catalytic oxidation of isobutene by uranium oxide. After being awarded his PhD, Dr Sears worked in process safety analysis (at Rhodia CSD and Thermal Hazard Technology) and in reaction optimisation and flow chemistry (at Syrris) before joining the defence science and technology laboratory (Dstl) in 2008. At Dstl, Dr Sears was a team leader in the Forensic Explosives Laboratory and latterly a Principal Scientist in Explosives Detection where his main research interests were in the analysis of trace explosive contamination and residues.
Affiliations and memberships
Dr Patrick Sears's research interests include:
- Understanding production, transfer, spread and fate of trace contamination (explosives, drugs, pharmaceuticals and within healthcare (bacteria and viruses))
- Developing methods and systems for the direct analysis of materials on surfaces
- Development of novel ionisation techniques for mass spectrometric analysis
- Understanding secondary ionisation processes
- Developing techniques for the forensic speciation of materials of interest
- Quantification of precision, accuracy and uncertainty of analytical systems of measurement
Dr Sears currently teaches on the following courses:
- CHE1039: Fundamentals of Forensic Science: From Crime Scene to Court
- SOC1042: Fundamentals of Forensic Science for Social Scientists
- CHE3055: Topics in Forensic Science*
- CHEM034: Advanced Methods in Forensic Investigation*
- CHE2033: Forensic Chemistry*
* indicates where Dr Sears is module leader
Five different classes of explosives were analysed by ambient ionisation mass spectrometry testing selectivity, sensitivity, and repeatability. We compare the effectiveness of two techniques (ASAP and SESI) for the trace detection of five explosives representative of the most common classes of high explosive: HMTD, RDX, PETN, Tetryl and TNT. Experiments also compared the effectiveness of sample loading via a glass fibre swab or glass rod. All analyses were carried out with a Waters Acquity QDa mass spectrometer, a small format mass spectrometer which can be operated in a transportable mode (using ambient air and a small diaphragm pump). Both ambient ionisation techniques, ASAP and SESI, successfully detected the five different explosives which could make them suitable for a screening method. By directly comparing a calibration range of 0.8–10 ng on both swabs and rods for each explosive, it appears that SESI produces less variability per repeat, particularly at the higher end of the range when compared to ASAP which typically has a lower limit of detection and better linearity.
Direct analyte probed nanoextraction (DAPNe) is a technique that allows extraction of drug and endogenous compounds from a discrete location on a tissue sample using a nano capillary filled with solvent. Samples can be extracted from a spot diameters as low as 6 µm. Studies previously undertaken by our group have shown that the technique can provide good precision (5%) for analysing drug molecules in 150 µm diameter areas of homogenised tissue, provided an internal standard is sprayed on to the tissue prior to analysis. However, without an isotopically labelled standard, the repeatability is poor, even after normalisation to and the spot area or matrix compounds. By application to tissue homogenates spiked with drug compounds, we can demonstrate that it is possible to significantly improve the repeatability of the technique by incorporating a liquid chromatography separation step. Liquid chromatography is a technique for separating compounds prior to mass spectrometry (LC-MS) which enables separation of isomeric compounds that cannot be discriminated using mass spectrometry alone, as well as reducing matrix interferences. Conventionally, LC-MS is carried out on bulk or homogenised samples, which means analysis is essentially an average of the sample and does not take into account discrete areas. This work opens a new opportunity for spatially resolved liquid chromatography mass spectrometry with precision better than 20%.
Paper spray mass spectrometry is a rapid and sensitive tool for explosives detection but has so far only been demonstrated using high resolution mass spectrometry, which bears too high a cost for many practical applications. Here we explore the potential for paper spray to be implemented in field applications with portable mass spectrometry. This involved (a) replacing the paper substrate with a swabbing material (which we call “swab spray”) for compatibility with standard collection materials; (b) collection of explosives from surfaces; (c) an exploration of interferences within a ± 0.5 m/z window; and (d) demonstration of the use of high-field assisted waveform ion mobility spectrometer (FAIMS) for enhanced selectivity. We show that paper and Nomex® are viable collection materials, with Nomex providing cleaner spectra and therefore greater potential for integration with portable mass spectrometers. We show that sensitive detection using swab spray will require a mass spectrometer with a mass resolving power of 4000 or more. We show that by coupling the swab spray ionisation source with FAIMS, it is possible to reduce background interferences, thereby facilitating the use of a low resolving power (e.g. quadrupole) mass spectrometer.
RATIONALE: Paper spray offers a rapid screening test without the need for sample preparation. The incomplete extraction of paper spray allows for further testing using more robust, selective and sensitive techniques such as liquid chromatography mass spectrometry (LC-MS). Here we develop a two-step process of paper spray followed by LC-MS to (1) rapidly screen a large number of samples and (2) confirm any disputed results. This demonstrates the applicability for testing medication adherence from a fingerprint. METHODS: Following paper spray analysis, drugs of abuse samples were analysed using LC-MS. All analyses were completed using a Q Exactive™ Plus Orbitrap™ mass spectrometer. This two-step procedure was applied to fingerprints collected from patients on a maintained dose of the antipsychotic drug quetiapine. RESULTS: The extraction efficiency of paper spray for two drugs of abuse and metabolites was found to be between 15-35% (analyte dependent). For short acquisition times, the extraction efficiency was found to vary between replicates by less than 30%, enabling subsequent analysis by LC-MS. This two-step process was then applied to fingerprints collected from two patients taking the antipsychotic drug quetiapine, which demonstrates how a negative screening result from paper spray can be resolved using LC-MS. CONCLUSIONS: We have shown for the first time the sequential analysis of the same sample using paper spray and LC-MS, as well as the detection of an antipsychotic drug from a fingerprint. We propose that this workflow may also be applied to any type of sample compatible with paper spray, and will be especially convenient where only one sample is available for analysis.
Publications from earlier in Dr Sears's career:
Performance validation of step-isothermal calorimeters: Application of a test and reference reaction. (2006) B.A. Finnin, M.A.A. O’Neill, S. Gaisford, A.E. Beezer, J. Hadgraft and P. Sears. J. Therm. Anal. Cal.83:331-334. https://doi.org/10.1007/s10973-005-7223-5
A Comparison of the performance of calorimeters: Application of a test and reference reaction. (2006) M.A.A. O’Neill, S. Gaisford, A.E. Beezer, C.V. Skaria, P. Sears. J. Therm. Anal. Cal. 84:301-306. https://doi.org/10.1007/s10973-005-7488-8
Kinetic Investigations of Product Inhibition in the Amino Alcohol-Catalyzed Asymmetric Alkylation of Benzaldehyde with Diethylzinc (2000) T. Rosner, P.J. Sears, W.A. Nugent, D.G. Blackmond. Organic Lett. 2:2551-2513. https://doi.org/10.1021/ol006181r
Synergic interactions in a urania–titania catalyst for isobutene partial oxidation. (2000) A.F.Lee, P.J. Sears, S.D. Pollington, T.L. Overton, P.B. Wells, D.F. Lee. Catal. Lett. 70:183-186. https://doi.org/10.1023/A:1018801804706
Novel supported uranium oxide catalysts for NOx abatement. (1999) S.D. Pollington, A.F. Lee, T.L. Overton, P.J. Sears, P.B. Wells, S.E. Hawley, I.D. Hudson, D.F. Lee, V.Ruddock. Chem. Commun., 1999, 725-726. https://doi.org/10.1039/A900802K