Alain Wuethrich

Chiral capillary electromigration techniques—mass spectrometry—hope and promise

Analytical methods for chiral compounds require a separation step prior to mass spectrometric detection. CE can separate enantiomers by the use of a chiral selector and can be hyphenated with MS. The chiral selector can be either embedded inside the capillary (electrochromatography) or added into the background solution (EKC). This review describes the fundamentals and highlights the recent developments (September 2009–May 2013) of chiral CEC and EKC with detection using MS. There were 20 research and more than 30 review papers during this period. The research efforts were driven by fundamental studies, such as the development of novel chiral selectors in electrochromatography and of advanced partial filling techniques in EKC in order to optimise separation. Other developments were in application studies, such as in food analytics and metabolomics.

Derivatisation for separation and detection in capillary electrophoresis (2012–2015)

Derivatisation is a well‐established and mature form of sample preparation for CE. The modification of the analyte can cause superior analysis characteristics such as better sensitivity and selectivity, however, derivatisation of the analyte introduces an additional step into the analytical workflow. This review covers articles from January 2012 to January 2015 on derivatisation in CE. The main sections are on the derivatisation modes (i.e. pre‐capillary, in‐line, in‐capillary and post‐capillary), separation and detection modes (i.e. LIF and others). LIF is discussed in more detail since this detection mode was most prevalent. A table of the common labelling agents and wavelengths for excitation and emission and the common derivatisation reactions are included. In addition, a comprehensive table which summarises all research articles is provided. This review is suitable for analytical chemists as a guide for ‘how to get started’ with derivatisation for separation and detection in CE.

Derivatisation for separation and detection in CE (2012‐2015)

Derivatisation is a well‐established and mature form of sample preparation for CE. The modification of the analyte can cause superior analysis characteristics such as better sensitivity and selectivity, however, derivatisation of the analyte introduces an additional step into the analytical workflow. This review covers articles from January 2012 to January 2015 on derivatisation in CE. The main sections are on the derivatisation modes (i.e. pre‐capillary, in‐line, in‐capillary and post‐capillary), separation and detection modes (i.e. LIF and others). LIF is discussed in more detail since this detection mode was most prevalent. A table of the common labelling agents and wavelengths for excitation and emission and the common derivatisation reactions are included. In addition, a comprehensive table which summarises all research articles is provided. This review is suitable for analytical chemists as a guide for ‘how to get started’ with derivatisation for separation and detection in CE.

Green sample preparation for liquid chromatography and capillary electrophoresis of anionic and cationic analytes

A sample preparation device for the simultaneous enrichment and separation of cationic and anionic analytes was designed and implemented in an eight-channel configuration. The device is based on the use of an electric field to transfer the analytes from a large volume of sample into small volumes of electrolyte that was suspended into two glass micropipettes using a conductive hydrogel. This simple, economical, fast, and green (no organic solvent required) sample preparation scheme was evaluated using cationic and anionic herbicides as test analytes in water. The analytical figures of merit and ecological aspects were evaluated against the state-of-the-art sample preparation, solid-phase extraction. A drastic reduction in both sample preparation time (94% faster) and resources (99% less consumables used) was observed. Finally, the technique in combination with high-performance liquid chromatography and capillary electrophoresis was applied to analysis of quaternary ammonium and phenoxypropionic acid herbicides in fortified river water as well as drinking water (at levels relevant to Australian guidelines). The presented sustainable sample preparation approach could easily be applied to other charged analytes or adopted by other laboratories.

Field-enhanced sample injection micelle-to-solvent stacking capillary zone electrophoresis-electrospray ionization mass spectrometry of antibiotics in seawater after solid-phase extraction

The synergistic stacking approach of field‐enhanced sample injection‐micelle‐to‐solvent stacking was used for high sensitivity CZE‐ESI‐MS of eight penicillins and sulfonamides. Sensitivity enhancement factors (peak height) were 1629–3328 compared to typical injection, with LODs from 0.11 to 0.55 ng/mL. The analytical figures of merit were acceptable. SPE on a fortified seawater sample resulted in 50‐fold enrichment with recoveries of 85–110%. The overall method LODs were 0.002–0.011 ng/mL.

Simultaneous electrophoretic concentration and separation of herbicides in beer prior to stacking capillary electrophoresis UV and liquid chromatography–mass spectrometry

Simultaneous electrophoretic concentration and separation (SECS) was used as a simple and environmental friendly sample preparation strategy for herbicides in beer samples. An electric field was used to facilitate the separation and concentration of the analytes based on their charge from a 20 mL sample of diluted beer into two separate 20 μL aliquots of an acceptor electrolyte housed inside a micropipette. The anionic organophosphonate and cationic quaternary ammonium herbicides were concentrated in the anodic and cathodic pipette, respectively. Under optimized conditions, SECS was completed in 30 min at an applied voltage of 150 V, which provided analyte concentration factors of up to 90. After sample preparation, the SECS concentrate of cationic and anionic herbicides was analyzed by stacking CE with UV detection and also by LC–MS, respectively. The method detection limit for the diluted and undiluted sample was as low as 3 and 15 ng/mL, respectively. The method was linear over two orders of concentration with repeatability and intermediate precision of better than 5.8 and 7.0%RSD, respectively. Accuracy values were between 91.0–115.1%.

Sensitivity enhancing injection from a sample reservoir and channel interface in microchip electrophoresis

The stacking of a cationic analyte (i.e., rhodamine B) at the interface between a sample reservoir and channel in a microchip electrophoresis device is described for the first time. Stacking at negative polarity was by micelle to solvent stacking where the dye was prepared in a micellar solution (5 mM sodium dodecyl sulfate in 25 mM phosphoric acid, pH 2.5) and the channel was filled with high methanol content background solution (70% methanol in 50 mM phosphoric acid, pH 2.5). The injection of the stacked dye into the channel was by simple reversal of the voltage polarity with the sample solution and background solution at the anodic and cathodic reservoirs of the straight channel, respectively. The enrichment of rhodamine B at the interface and injection of the stacked dye into the channel was clearly visualized using an inverted fluorescence microscope. A notable sensitivity enhancement factor of up to 150 was achieved after 2 min at 1 kV of micelle to solvent stacking. The proposed technique will be useful as a concentration step for analyte mixtures in simple and classical cross-channel microchip electrophoresis devices or for the controlled delivery of enriched reagents or analytes as narrow plugs in advanced microchip electrophoresis devices.

Interfacial nano-mixing in a miniaturised platform enables signal enhancement and in situ detection of cancer biomarkers

Interfacial biosensing performs the detection of biomolecules at the bare-metal interface for disease diagnosis by comparing how biological species derived from patients and healthy individuals interact with bare metal surfaces. This technique retrieves clinicopathological information without complex surface functionalisation which is a major limitation of conventional techniques. However, it is still challenging to detect subtle molecular changes by interfacial biosensing, and the detection often requires prolonged sensing times due to the slow diffusion process of the biomolecules towards the sensor surface. Herein, we report on a novel strategy for interfacial biosensing which involves in situ electrochemical detection under the action of an electric field-induced nanoscopic flow at nanometre distance to the sensing surface. This nanomixing significantly increases target adsorption, reduces sensing time, and enables the detection of small molecular changes with enhanced sensitivity. Using a multiplex electrochemical microdevice that enables nanomixing and in situ label-free electrochemical detection, we demonstrate the detection of multiple cancer biomarkers on the same device. We present data for the detection of aberrant phosphorylation in the EGFR protein and hypermethylation in the EN1 gene region. Our method significantly shortens the assay period (from 40 min and 20 min to 3 minutes for protein and DNA, respectively), increases the sensitivity by up to two orders of magnitude, and improves detection specificity.

A SERS microfluidic platform for targeting multiple soluble immune checkpoints

Immune checkpoint blockade therapies are promising next generation immunotherapeutic treatments for cancer. Whilst sequential solid biopsies are an invaluable source of prognostic information, they are not feasible for monitoring therapeutic outcomes over time. Monitoring soluble immune checkpoint markers expression in body fluids could potentially be a better alternative. Current methods (e.g. ELISA) for detecting immune-checkpoint proteins mostly rely on the use of monoclonal antibodies which are expensive and time-consuming to manufacture and isolate. Herein, we report an integrated surface enhanced Raman scattering (SERS)-microfluidics device for the detection of immune checkpoint proteins which involves the use of i) nano yeast single chain variable fragment (scFv) as a promising alternative to monoclonal antibodies providing high stability at relative low-cost and simplicity for production, ii) graphene oxide functionalised surface to reduces the bio functionalization steps, thus avoiding the general paradigm of biotin-streptavidin chemistry and iii) a microfluidic platform enabling alternating current electrohydrodynamics (ac-EHD) induced nanomixing to enhance the target scFv binding and minimize the non-specific interactions. Specific and multiplex detection of immune checkpoint biomarkers is achieved by SERS based spectral encoding. Using this platform, we successfully demonstrated the detection of clinically relevant soluble immune checkpoints PD-1, PD-L1 and LAG-3 from as low as 100 fg/mL of analytes spiked in human serum.

A decade of microchip electrophoresis for clinical diagnostics – A review of 2008–2017

A core element in clinical diagnostics is the data interpretation obtained through the analysis of patient samples. To obtain relevant and reliable information, a methodological approach of sample preparation, separation, and detection is required. Traditionally, these steps are performed independently and stepwise. Microchip capillary electrophoresis (MCE) can provide rapid and high-resolution separation with the capability to integrate a streamlined and complete diagnostic workflow suitable for the point-of-care setting. Whilst standard clinical diagnostics methods normally require hours to days to retrieve specific patient data, MCE can reduce the time to minutes, hastening the delivery of treatment options for the patients. This review covers the advances in MCE for disease detection from 2008 to 2017. Miniaturised diagnostic approaches that required an electrophoretic separation step prior to the detection of the biological samples are reviewed. In the two main sections, the discussion is focused on the technical set-up used to suit MCE for disease detection and on the strategies that have been applied to study various diseases. Throughout these discussions MCE is compared to other techniques to create context of the potential and challenges of MCE. A comprehensive table categorised based on the studied disease using MCE is provided. We also comment on future challenges that remain to be addressed.