On-site Analytical Chemistry (dr. GIJ (Gert) Salentijn)

BIO-SKETCH

Dr. Gert Salentijn is assistant professor in Analytical Chemistry at Wageningen University & Research (both in the Lab of Organic Chemistry and in the Biosensors group at Wageningen Food Safety Research) and a 2019 recipient of the NWO Veni grant. In 2019 he worked as a visiting scientist in the world’s leading mass spectrometry group of Prof. Graham Cooks at Purdue in the USA. He is Work Package leader for detection technology in the Horizon 2020 ITN FoodSmartphone. He teaches in three chemistry courses; analytical methods in organic chemistry (BSc course), environmental analytical techniques (MSc course), and advanced (bio)analytical chemistry (elective).

Gert Salentijn obtained his MSc degree in Pharmacy cum laude at the University of Groningen, and completed his PhD cum laude in the Verpoorte group in Groningen in a public-private partnership (NWO-COAST) to develop portable ion sources for mass spectrometry (MicroMS). He has co-founded SG Papertronics, a spin-off company from the University of Groningen, developing platform technology for paper-based analyses, based on his patented technology for sample pre-concentration on paper.

In his past research, Gert Salentijn has pioneered the application of 3D-printing for functionalized, microfluidic devices, and contributed substantially to the advancement of paper spray ionization, an ambient ionization method for mass spectrometry. Simultaneously, he has developed a separate research line in which surface modification of paper is employed to create smart on-site testing.

All current research in his team is ultimately aimed at getting chemical analysis out of the lab, and into the hands of the people that need the (interpretation of) chemical information. These could be consumers that want to know that their food can be safely eaten (e.g. free from allergens or contaminants), inspectors that need to monitor food safety for the government, or patients who need to know vital information about their own health. Different research fields and analytical strategies are combined to achieve such goals, including ambient ionization (portable) mass spectrometry, lateral flow immunochemistry, chemical surface modification for (paper) microfluidics and 3D-printing.

RESEARCH LINES: RECENT DEVELOPMENTS AND FUTURE DIRECTIONS

Biosensors for consumer diagnostics

One of the hallmarks of on-site analytical chemistry is the pregnancy test. The concept of the test, a lateral flow immunoassay (LFIA), is still very relevant today. We explore the use of the LFIA for ultra-fast detection of allergenic proteins in food samples, in combination with innovative 3D-printed modules for extraction and sample handling, and smartphones for data analysis and semi-quantitative readout. This total-analysis system approach can be readily adapted to different application fields and sample types. Additionally, we are starting to explore isothermal amplification in combination with lateral flow readout. Finally, future research will include the development of novel detection mechanisms that can be used in such user-friendly assays to improve sensitivity.

Stimuli-responsive paper microfluidics

The above-mentioned LFIAs and other biosensors are mature techniques that can be readily applied to on-site analysis, for example for food safety. However, the assays are limited by the used materials and device configurations (rectangular strip made from nitrocellulose with test and control lines). In the research field known as paper microfluidics, we work on designing innovative device functionality, such as on-paper valves, multiphase extractions, and self-directing sample flows – ultimately to create better materials for on-site testing. Here, the aim is twofold: (i) research into alterative materials for ‘paper’ microfluidics, and (ii) employ cutting-edge surface chemistry to develop smart, responsive paper-based systems.

Ambient Ionization Mass Spectrometry

While LFIAs and other paper-based tests are very useful in the development of on-site screening methods, mass spectrometry is still the golden standard in analytical chemistry, with its superior sensitivity and resolution, and the powerful combination with instrumental chromatography. However, this is only feasible in a well-equipped laboratory. To bridge the gap between on-site screening and powerful lab-based analysis, there is substantial development going on towards portable mass spectrometry combined with ambient ionization. Ambient ionization allows one to create gas-phase ions from a sample in a straightforward manner, under ambient conditions. An important member of this family is paper spray ionization, where a simple paper tip can be used to generate the ions from a sample spot by application of a high potential. Ongoing research is focused on the chemical modification of paper to create specific surfaces that can capture the chemicals of interest, while discarding most of the contaminants and interferants, prior to mass spectrometric analysis.

3D-printing for analytical chemistry

3D printing is a collection of techniques that allows one to iteratively move through the design-produce-test-evaluate cycle at an unprecedented pace, leading to ultra-rapid prototyping. We use 3D-printing to rapidly develop devices, often in combination with paper-based assays, to increase the functionality of such tests, and make them easier to use by integration and encasing them. Examples hereof are cartridges for paper spray ionization mass spectrometry that help to improve spray duration and stability, and modules that facilitate the on-site extraction and quantitative dilution of samples for analysis by non-experts for LFIA.