Abstract
Even though numerous methods have been developed for the detection and quantification of waterborne pathogens, the application of these methods is often hindered by the very low pathogen concentrations in natural waters. Therefore, rapid and efficient sample concentration methods are urgently needed. Here we present a novel method to pre-concentrate microbial pathogens in water using a portable 3D-printed system with super-absorbent polymer (SAP) microspheres, which can effectively reduce the actual volume of water in a collected sample. The SAP microspheres absorb water while excluding bacteria and viruses by size exclusion and charge repulsion. To improve the water absorption capacity of SAP in varying ionic strength waters (0–100 mM), we optimized the formulation of SAP to 180 g⋅L−1 Acrylamide, 75 g⋅L−1 Itaconic Acid and 4.0 g⋅L−1 Bis-Acrylamide for the highest ionic strength water as a function of the extent of cross-linking and the concentration of counter ions. Fluorescence microscopy and double-layer agar plating respectively showed that the 3D-printed system with optimally-designed SAP microspheres could rapidly achieve a 10-fold increase in the concentration of Escherichia coli (E. coli) and bacteriophage MS2 within 20 min with concentration efficiencies of 87% and 96%, respectively. Fold changes between concentrated and original samples from qPCR and RT-qPCR results were found to be respectively 11.34–22.27 for E. coli with original concentrations from 104 to 106 cell·mL−1, and 8.20–13.81 for MS2 with original concentrations from 104 to 106 PFU·mL−1. Furthermore, SAP microspheres can be reused for 20 times without performance loss, significantly decreasing the cost of our concentration system.
Highlights
Waterborne pathogens, including various pathogenic bacteria, viruses, and protozoa, are responsible for a series of diseases, and have been a major public health concern worldwide [1,2,3]
Variances in the porous polymer structure during drying of each polymer microspheres may lead to slight density inconsistency between microspheres, but these slight differences in shape and density would not influence the performance of superabsorbent polymer (SAP) microspheres on water absorption as they became uniform after they start to absorb water
Our results showed that the tube concentration system based on SAP microspheres could achieve satisfactory concentration efficiencies of E. coli solutions with a range of initial concentrations
Summary
Waterborne pathogens, including various pathogenic bacteria, viruses, and protozoa, are responsible for a series of diseases, and have been a major public health concern worldwide [1,2,3]. According to the World Health Organization (WHO), global mortality attributable to water-related diseases is currently 3.4 million per year, most of which are children [4]. This issue is especially severe in developing regions of the world due to the scarcity of clean water supplies and poor sanitation conditions [1,4,5,6]. Sensitive detection and quantification methods for waterborne pathogens, including traditional culture-based methods, or more recently, nucleic acid amplification tests [3,7,8,9,10], are indispensable to ensure water safety and to protect the public health. Pathogen concentrations below the detection limit of the methods mentioned above, do not guarantee the safety of water, as they may still pose a health risk considering their low infectious doses [5,11]
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