By: Florenda S. Valera, Ph.D.
KKP-DAS Vice Chair
The Kapisanang Kimika ng Pilipinas – Division of Analytical Science (KKP-DAS) organized a webinar “Chemical Sensors and Sensing Devices” on August 17, 2022 via Webex. The webinar was the 5th of a series of webinars this year in celebration of the 85th Anniversary of the Kapisanang Kimika ng Pilipinas (KKP) – Walumpu’t limang taon ng Kagalingan ng Kimikong Pinoy. The Chemistry Department of the University of Santo Tomas co-sponsored the webinar. It was well attended by about 170 participants all over the Philippines. There was good representation from Luzon, Visayas and Mindanao.
Chemical sensors provide a convenient and rapid way to detect analytes in a wide range of applications – environmental samples, agriculture, food safety, and healthcare. They are relatively easy to fabricate using inexpensive materials. There is growing interest in producing sensing devices with improved sensitivity and selectivity. Incorporation of nanomaterials in sensing devices has greatly improved sensing efficiency.
The topic “Carbon-Polymer Composite Systems as Sensor Electrode for Various Electroanalytical Sensing Applications” was presented by Dr. Allan Christopher C. Yago, Associate Professor at the Institute of Chemistry, University of the Philippines-Diliman. The carbon-polymer composite system is a combination of a carbon source (carbon nanotubes, powder graphite, graphene) and a viscous polymer (polydimethylsiloxane, polyvinylpyrrolidone, polycaprolactone). Dr. Yago discussed the (1) preparation of the carbon-polydimethylsiloxane (C-PDMS) composite electrode by direct mixing, placing in a 1.00 mL syringe and putting a Cu wire, (2) activation of the electrode by potentiodynamic cycling (anodization), (3) characterization of the electrode (electrochemical – specific capacitance, EIS, cyclic voltammetry; and chemical – FTIR, Raman, SEM, bulk conductivity), and (4) optimization of conditions for target molecules detection by modifying surface or bulk composition. C-PDMS has been shown to have better electrochemical properties than the conventional glassy carbon electrodes. Carbon nanotube – polydimethylsiloxane (CNT-PDMS) composite electrode can be used to detect various organic and bio-organic molecules like ascorbic acid, dopamine, uric acid, pesticides (chlorpyrifos, fenthion), and methylene blue aqueous dye. Uric acid was detected using a uricase-metal oxide-modified CNT-PDMS biosensor. A Bismuth(III) – modified CNT-PDMS was used for simultaneous detection of inorganic metals Cadmium(II) and Zinc(II). Dr. Yago was able to develop a utility model (Philippines) – Carbon Electrodes for Sensitive Detection of Pesticides and Other Substances. CNT-PDMS can be used as screen-printed electrode format. The composite electrodes can be stored and reused.
The topic “Microfluidic Paper-Based Devices (mPADs) and their Applications in Food Safety and Environmental Monitoring” was presented by Dr. Lori Shayne A. Busa, Associate Professor at the Nueva Vizcaya State University in Bayombong, Nueva Vizcaya. Some of the applications of mPADs are in clinical diagnostics, environmental monitoring, veterinary medicine, bioterrorism, and food and nutrition safety. The advantages of mPADs include the use of inexpensive materials, cost-effective manufacturing processes, point-of-need applications, small amounts of reagents needed, little or no external supporting equipment or power, rapid detection, portable and easy to use device. Dr. Busa developed a simple horseradish peroxidase (HRP) assay system on mPADs for point-of-need testing in food monitoring. She fabricated mPADs by photolithography using paper substrate (FP41) and employed colorimetric detection for horseradish peroxidase (HRP) after its reaction with a chromogenic substrate such as 3,3’,5,5’-tetramethylbenzidine (TMB). The developed HRP assay system on mPADs was applied in competitive immunoassay for target antigens. Aflatoxin B1 was detected in food samples using competitive assay. Compared to ELISA kit (conventional method), mPAD uses less volume, faster assay time, and cheaper cost per assay. Dr. Busa was able to develop three mPADs by ink-jet printing using paper substrate (FP41) and colorimetric detection for diarrhea-causing pathogens like E. coli in water samples. Applications for IP registration for the three devices are being processed. The first device used paper-based chlorophenol red-β-D-galactopyranoside (CPRG) assay; the second device used biochemical-based (Rose-gal) assay system detection mechanism; and the third device used sandwich immunoassay using biotin and streptavidin. The three devices for E. coli detection compared favorably with UNICEF methodologies; analysis time was shorter, little or no training of personnel, and cost per assay was cheaper.
The topic “Recent Advances and Future Prospects of Sensing Devices” was presented by Dr. Rey Y. Capangpangan, Professor at Mindanao State University-Naawan. Dr. Capangpangan’s research incorporates nanoparticles in paper-based sensors for rapid sensing of analytes. On-site detection of copper ions was achieved by functionalizing silver nanoparticles on paper substrates. A sensor was developed for the determination of cyanide from mining samples by depositing gold nanoparticles on paper substrates and using colorimetric detection. Remote continuous monitoring of cyanide was achieved using a CYANanobot. A direct immersion process for immobilizing silver nanoparticles was also developed for the determination of cyanide. A paper-based sensor for mercury was developed using thiamine functionalized silver nanoparticles with colorimetric detection; automation of this sensor is in process. Paper sensors for lead, cadmium and nickel were also developed with modifications for gold and silver nanoparticles to increase the selectivity of the sensors towards these target analytes. Aside from environmental samples, Dr. Capangpangan is also working on rapid sensing kits for food spoilage monitoring. Fabrication of paper-based sensors is basically the same as that used in environmental samples. Plasmonic nanomaterials (gold, silver) will be deposited on paper substrates, ligands and probably aptamers will be attached to improve sensor selectivity. Dr. Capangpangan has patent applications for the finished paper-based sensors. Future perspectives involve collaboration with other research institutions. Project SMIDERM (Smart Multifunctional and Indigenous Dressings sterilized under an Electron beam as novel wound Repair Matrices) is in Phase I (Biomedical device development and characterization). Project TANIM (Transformative Agriculture through Nanotechnology in Mindanao) is intended to address important issues in Agriculture such as promoting sustainable agriculture, climate-resilient and high yield crops, pest control, precision agriculture, and disease-resistant plants. Project nano-ISDA (Innovative and Sustainable (nanomaterial) Design for Aquaculture) will address fish health, water quality (remediation), nutrient controlled release, biosensors, and toxicity evaluation. As part of the National Center for Sustainable Polymers R & D (NCSP-R&D), Dr. Capangpangan’s team is working on the production of polymeric materials from waste materials and development of polymeric-based sensors from indigenous sources.