Analytical Chemistry

Na Li is a Professor at the College of Chemistry and Molecular Engineering, Peking University. She obtained her BS (1988), MS (1991) and PhD (1994) degrees from Peking University. Her current research interests are optical sensing methods and applications with the major interest in nanoparticle-based spectroscopy (fluorescence, localized surface plasmon resonance absorption or light-scattering) and the application in biosensing.

Single-particle based counting is but one approach to achieve high sensitivity hopefully without the aid of target amplification. In the efforts towards single particle counting based biosensing, we have developed algorithm for dark-field microscope imaging based gold nanoparticle counting. By calibration using reference gold nanoparticles, the counting accuracy was improved, and the versatility of the established counting platform was demonstrated with applications for nucleic acids and biomarker detection. With very simple experimental implementation with target or signal amplification, high sensitivity with a limit of detection as low as femtomolar was achieved for nucleic acid detection. In many situations such as diagnosis and therapy of human diseases, the sensitive multiplexed detection of targets in a single sample by a simple manner is most desirable. To extend the counting strategy to multiplexed detection, an automatic fluorescent nanoparticle (FNP) counting platform was developed with a common fluorescence microscopic imaging setup for non-amplification multiplexed detection of nucleic acids. Quantification for multiplex nucleic acids, including DNAs, microRNAs (miRNA), as well as the DNA and miRNA mixture was achieved with the limit of detection down to 5 amol (5-L detection volume), and the 81 115% spike recovery from different biological sample matrices. We further developed a multiplex SNV detection method that combines the masking tactic with FNP counting based on the sandwich design. With the discrimination factor ranged from 204 to 1177, as low as 0.05% abundance was successfully identified for most cases. The single nanoparticle counting with microscopic imaging shows potentials for simple and highly sensitive biosensing applications. Efforts are under the way to further improve the counting fidelity and sensitivity by working on the counting algorithm, nanoparticles and strategies.

Ewelina Patyra has completed her PhD in Analytical Chemistry in National Veterinary Research Institute in Pulawy, Poland and Postdoctoral training in University Santiago de Compostela in Lugo Spain. She has worked in University of Life Sciences in Lublin, Poland and Laboratoire d’Etude des Residus et Conataminants dans les Aliments in Nantes, France. Currently she works as an Assistant Professor in Department of Hygiene of Animal Feeding stuffs National Veterinary Research Institute in Pulawy, Poland. Her main subject of work is development of new analytical methods in detection of antibacterial substances in animal feeds and manure with the use of liquid chromatography techniques.

Veterinary antibiotics are used globally to treat disease and to protect the health of animals. Antibiotics that are frequently used in livestock are tetracyclines, sulfonamides and fluoroquinolones, which are active against gram-negative and gram-positive bacteria. After administration of antibiotics, 30–90% of the dose given is excreted in non-metabolized form or as active metabolites and as a result high levels of antibiotics and active metabolites are expected to be present in faeces. Currently land application of manures is common practice in many parts of the world, including Poland. Liquid manure is characterized by a high nutrient content making it valuable as a soil fertilize. However if animals are medicated, residues of the pharmaceuticals can frequently be detected in manure due to poor absorption of the respective substance in the animal gut or unmetabolized extraction. The residue levels of selected fluoroquinolones, tetracyclines, trimethoprim, tylosin and tiamulin in 30 animal dung and liquid manure samples and collected in 2018 from large-scale livestock in Poland. The sample preparation was made by using ultrasonic extraction with Mcilvaine-Na2EDTA buffer solution and purified by SPE (Strata-X-CW cartridges) and analysed by HPLC-MS. Validation of the method was performed according to the guidelines indicated in European Commission Decision 2002/657/EC. Recoveries from spiked pig and poultry dung and liquid manures samples ranged from 76.1 to 112.0% for all analysed antibacterial substances. Method quantification limits were in the range from 23.1 to 72.3 μg/kg for tetracyclines, fluoroquinolones, trimethoprim, tylosin and tiamulin. Analysis of 30 pig and chicken dung and liquid manure samples collected in Poland revealed that 11 samples were positive for the presence of doxycycline, enrofloxacin, oxytetracycline and tylosin. These analytes were detected in maximum concentrations reaching up to 4100 μg/kg (doxycycline).