Cost-effective smart microfluidic device with immobilized silver nanoparticles and embedded UV-light sources for synergistic water disinfection effects

A novel microfluidic-device for water disinfection via diverse physiochemical effects has been demonstrated. Firstly, a microfluidic device with embedded, multiple germicidal UV-LEDs was fabricated through the innovatively modified cost-effective soft-lithography process. Further, synthesised silver nanoparticles were immobilized within its inner microchannel surface. Disinfection results proved the synergistic bactericidal effect of coated AgNPs and coupled UV-light, while a suspension of bacterial strains, were passed through the micro-device.

A novel microfluidic-device for water disinfection via diverse physiochemical effects has been demonstrated.

The expansion of micro-devices, with different functionalities, is the need of the hour. In particular, cost-effective disinfection of water can profoundly affect the health of the developing world particularly children and is expected to have a huge market. Currently, a large number of water purification systems are commercially available, with effective performance; however, they are exceedingly costly and have heavy maintenance costs for their successful operation. In various distinct approaches a UV light source or silver metal has been used for water purification in large scale water purification systems.In one of the earlier studies, the antimicrobial activity of a doped hydroxyapatite/polydimethylsiloxane (Ag: HAp-PDMS) composite layer, obtained by the thermal evaporation technique, proved to be active against Candida albicans.¹ According to Shekhar Agnihotri et. al., the bacteriostatic/bactericidal effect of AgNPs were size and dose-dependent and for AgNPs.² However, in these studies, they did not immobilize the nanoparticles on any surface, rather they have directly used the nanoparticles in suspension-form to conduct the analysis.² Ping Y. Furlan et. al. designed a bifunctional activated carbon nanocomposite with incorporated nanoscale-sized magnetic magnetite and antimicrobial silver nanoparticles (MACAg) and tested its antimicrobial efficacy against Escherichia coli (E. coli). They concluded that only Ag nanoparticles and Ag⁺ ions showed antimicrobial activities.³ Joong Hyun Kim et. al., conducted in situ fabrication of AgNPs on the surface of PDMS and found the effective antibacterial activity of the nanocomposites against both E. coli and S. aureus. Also, the nanocomposites were observed to have no cellular toxicity and thus could be used as implants for medical devices.⁴ G. Ipek Yucelen and team presented a novel approach to synthesize silver nanoparticles on aluminosilicate nanotubes by decomposition of AgNO₃ solution to AgNPs at room temperature and found this hybrid to show strong antibacterial activity towards Staphylococcus epidermidis and Escherichia coli.⁵ The AgNP sheets (AgNPs deposited on the cellulose fibres of an absorbent blotting paper) exhibited antibacterial properties toward suspensions of Escherichia coli and Enterococcus faecalis, when these pathogenic bacteria were inactivated during percolation through the sheet.⁶ A water filter was coated with silver paint to form silver ions (Ag⁺) for killing the bacteria present in dirty water and make it drinkable. An overview of nanomaterials for water and wastewater treatment had been recently presented by Haijiao Lu et al.⁷ Alexandru Rus et. al. designed a filter using additive manufacturing techniques and coated it with different concentrations of silver solutions.⁸The performance of the world''s first commercial UV-C LED water disinfection reactor (the Pearl Aqua by Aquisense) was compared with an existing chlorination system and all the tests showed the reactor equivalent to the chlorination system in all aspects.⁹ Andrej Gross and team investigated light guidance capabilities of optical pure quartz glass with UV-C LEDs and found the system to show increased disinfection efficiency when tested against Escherichia coli and Bacillus subtilis.¹⁰ In this approach, they have used the phenomenon of total internal reflection of UV-C irradiation for disinfecting water, in which they have coupled UV-C LEDs to a quartz tube and a glass tube for conducting the analysis.¹⁰Further, none of the abovementioned approaches, in earlier reported study, has demonstrated the cumulative disinfection effect of UV-light source, as well as, silver nano-particle, at micro-scale. Unfortunately, none of the existing water disinfection methods provides a crucial combination of key requirements such as high antimicrobial efficiency, low cost, easy maintenance and scalability to both small and large scale. In our premiere approach, a novel cost-effective microfluidic device for water disinfection, with multiple physiochemical effects has been projected in the current study for effective and faster disinfection.The water disinfection system described here, resolves such problems by providing a simple, cost-effective and efficient water disinfection method with the utilization of silver nanoparticles and ultraviolet (UV) light in a microfluidic system via a synergistic effect. The bacteria-infested water was disinfected in the microscopic volumes per unit time. Further, similar multiple microchannels can be arranged in a parallel manner to obtain the required flow rate and quantity of water, needed to be disinfected. The system also ensures safety against silver leakage and excessive human exposure to ultraviolet (UV) light.