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Papers by FORTUNATO SEVILLA

An electronic nose based on piezoelectric quartz crystal was developed for monitoring the maturat... more An electronic nose based on piezoelectric quartz crystal was developed for monitoring the maturation of carabao mango. This device detects the volatile organic compounds present in the headspace of the mango fruit. The crystals were coated with different organic organic polymers that interact with the volatile organic compounds, and this interaction was monitored through a self-assembled instrumentation and recorded by a computer in terms of frequency change. The quartz sensors gave stable response to the mango fruit sample, exhibited good repeatibility (r.s.d. = 3.3 to 5.5%, n=3) and good reproducibility (r.s.d. = 1.9 to 6.1%, n=5). Different signals were observed at different stages of the maturation of carabao mango fruit. The application of principal component analysis (PCA) enabled the discrimination of the responses of the electronic nose to mango fruits at different stages of maturation.

Holzforschung, 2018

Fast and efficient alternative methods for wood species identification are needed to combat illeg... more Fast and efficient alternative methods for wood species identification are needed to combat illegal logging and to control fair trade. One of the possibilities of rapid wood recognition is via chemiresistor gas sensor arrays (“electronic nose”), the application of which is described in the present paper. Carbon nanotube composites (CNTs) of eight insulating polymers were prepared through solution processing and spin casting. The optimum amount of CNTs in the composites was determined by resistance measurement and the CNTs were characterized by scanning electron microscopy. In the case of static headspace analysis, the sensor responses were reproducible and discernible for the wood species. This was demonstrated based on five wood species (Pterocarpus indicus, Acacia auriculiformis, Gmelina arborea, Vitex parviflora and Diospyros philippinensis). Discrimination of the data was achieved through principal component analysis (PCA) and hierarchical cluster analysis (HCA). PCA score plots...

Mikrochimica acta, Jan 10, 2018

A chemiresistor sensor for ultra-low levels of elemental mercury (Hg) vapor is described. The sen... more A chemiresistor sensor for ultra-low levels of elemental mercury (Hg) vapor is described. The sensor was prepared through thermal reduction of graphene oxide (GO) deposited on an interdigitated electrode using only low temperature annealing typically at 230 °C. The sensor responds to the presence of Hg vapor within <1 min and spontaneously recovers its baseline through flushing with a Hg-free carrier gas. The sensor has a linear response in the range of 0.5 to 12.2 ppb of Hg vapor and a detection limit of 0.10 ppb. The amount of GO and annealing temperature affect the sensor response and were optimized. The sensor can find use in monitoring exposure of persons to Hg vapors, for which a threshold value of 6.1 ppb has been set by the World Health Organization. Graphical abstract Schematic of an interdigitated electrode modified with a layer of thermally reduced graphene oxide. It can be used as a chemiresistive sensor for Hg vapor. The sensor displays a rapid and reversible respons...

Talanta, 1988

The Alizarin Fluorine Blue method for the determination of fluoride has been adapted for use with... more The Alizarin Fluorine Blue method for the determination of fluoride has been adapted for use with optical fibres. The reagent was immobilized on a polymer matrix, Amberlite XAD-2, and the reflectance of this reagent phase was measured as a function of fluoride concentration by use of a flow-cell assembly and a bifurcated fibre-optic system. A linear response was obtained for 0.16-0.95mM fluoride at a pH of 4.1, with a response time of approximately 12 min.

Journal of Physics E: Scientific Instruments, 1988

... The feasibility of using optical fibre sensors for monitoring ground-water contaminants has b... more ... The feasibility of using optical fibre sensors for monitoring ground-water contaminants has been demonstrated. For example, a spectroscopic sensor has been employed for the remote detection of phenolic contaminants in ground-water (Chudyk et a1 1985). ...

Analytical and bioanalytical chemistry, 2017

Current glucose monitoring techniques for neonates rely heavily on blood glucose monitors which r... more Current glucose monitoring techniques for neonates rely heavily on blood glucose monitors which require intermittent blood collection through skin-penetrating pricks on the heel or fingers. This procedure is painful and often not clinically conducive, which presents a need for a noninvasive method for monitoring glucose in neonates. Our motivation for this study was to develop an in vitro method for measuring passive diffusion of glucose in premature neonatal skin using a porcine skin model. Such a model will allow us to initially test new devices for noninvasive glucose monitoring without having to do in vivo testing of newborns. The in vitro model is demonstrated by comparing uncompromised and tape-stripped skin in an in-line flow-through diffusion apparatus with glucose concentrations that mimic the hypo-, normo-, and hyper-glycemic conditions in the neonate (2.0, 5.0, and 20 mM, respectively). Transepidermal water loss (TEWL) of the tape-stripped skin was approximately 20 g m(-2...

Food Chemistry, Function and Analysis, 2016

This chapter provides an overview of recent progress towards the design, synthesis, and applicati... more This chapter provides an overview of recent progress towards the design, synthesis, and application of molecularly imprinted polymers (MIPs) as food biosensors. Molecular imprinting is an innovative approach for mimicking natural molecular recognition processes through the preparation of synthetic recognition systems. MIPs are rapidly becoming viable alternatives to natural antibodies for sensor technology. The use of MIPs as sensors for determining the presence of contaminants in food has attracted considerable interest from numerous researchers and earned these materials a special niche as analytical devices for assessing food safety. Research on MIPs is an evolving field with a wide range of applications in manufacturing, processing, analysis, and quality control of foodstuffs. MIPs have several advantages for these uses, including high sensitivity, selectivity and portability, as well as their requirement for small samples. A variety of different transducers have been developed for food sensing, including optical, electrochemical, and mass-based sensors, which are discussed in detail in this chapter.

Talanta, 2017

Headspace Fourier Transform Infrared Spectroscopy (HS-FTIR) in tandem with chemometrics was appli... more Headspace Fourier Transform Infrared Spectroscopy (HS-FTIR) in tandem with chemometrics was applied to differentiate several species of the genus Pandanus. The headspace was generated from each Pandanus sample after incubation in a tightly sealed sample chamber. The resulting FTIR spectra of the headspace samples were found to be almost similar, but the application of principal component analysis (PCA) effectively differentiated the species. The unique spectral features for some samples were highlighted in the second-derivative FTIR spectra. A higher variance was exhibited in the PCA bi-plot of the 2nd derivative spectral data. The principal components differentiated not only the species, but also the cultivars or varieties, which formed distinct but proximate clusters. The manner of clustering obtained in this study resembled the behavior reported in a Random Amplified Polymorphic DNA analysis conducted on the Pandanus samples. The results demonstrate the potential of headspace FTIR spectroscopy as a simple, rapid, non-destructive, and relatively inexpensive method to discriminate between plant species and varieties.

Academic Research International

ABSTRACT

The Analyst, 1986

Several reagent systems, such as 2,6-dichlorophenolindophenol, phenanthroline complexes and dithi... more Several reagent systems, such as 2,6-dichlorophenolindophenol, phenanthroline complexes and dithiofluorescein complexes, have been immobilised on polymeric solid supports and their suitability as interphases in optical fibre sensors for sulphide ions investigated. These studies were carried out in a flow cell arrangement. The reflectance of the reagent phase was measured using optical fibres and was found to be related to the concentration of the sulphide ions in the solution. The dynamic range for sulphide ion determination varied with the reagents. The reagent phases prepared from 2,6-dichlorophenolindophenol and from the complex formed by dithiofluorescein with o-hydroxymercuribenzoic acid could be regenerated and are considered suitable for the development of an optical fibre sensor for sulphide ions.

Talanta, 2016

An array of chemiresistors based on conducting polymers was assembled for the differentiation of ... more An array of chemiresistors based on conducting polymers was assembled for the differentiation of coconut oil products. The chemiresistor sensors were fabricated through the potentiostatic electrodeposition of polyaniline (PANi), polypyrrole (PPy) and poly(3-methylthiophene) (P-3MTp) on the gap separating two planar gold electrodes set on a Teflon substrate. The change in electrical resistance of the sensors was measured and observed after exposing the array to the headspace of oil samples. The sensor response was found rapid, reversible and reproducible. Different signals were obtained for each coconut oil sample and pattern recognition techniques were employed for the analysis of the data. The developed system was able to distinguish virgin coconut oil (VCO) from refined, bleached &amp;amp;amp;amp;amp;amp; deodorised coconut oil (RBDCO), flavoured VCO, homemade VCO, and rancid VCO.

2005 Asian Conference on Sensors and the International Conference on New Techniques in Pharmaceutical and Biomedical Research

ABSTRACT A biomimetic caffeine sensor based on conducting polymers was fabricated by integrating ... more ABSTRACT A biomimetic caffeine sensor based on conducting polymers was fabricated by integrating the molecularly imprinted polymer (MIP) with a piezoelectric quartz crystal. This was achieved through galvanostatic electrodeposition of the MIP directly onto one electrode of the quartz crystal in the presence of a template caffeine molecule. Electropolymerization parameters for poly(o-phenelynediamine) (PoPD) and polypyrrole (PPy) were optimized. The sensors exhibited a linear relationship between the frequency shift and the logarithm of the caffeine concentration from 0.1 to 10 mg/mL. Correlation coefficients observed for the sensors based on PoPD and PPy were 0.9923 and 0.9888 respectively. The steady state response (∼10 min) achieved was similar for both sensors. The sensitivity of PoPD-based sensor (130 Hz/ ln conc. (mg/mL) was about half of that for the sensor based on PPy (255 Hz/ln conc. (mg/mL). A good repeatability (rsd = 9 %) was obtained for both sensors using 0.5 mg/mL caffeine solution.

2015 XVIII AISEM Annual Conference, 2015

ABSTRACT A water dispersible graphene polymer nanocomposite was synthesized by solution blending ... more ABSTRACT A water dispersible graphene polymer nanocomposite was synthesized by solution blending method and deposited on a nylon-6 membrane via vacuum assisted self-assembly (VASA) method to fabricate a flexible material applied as a chemoresistive gas sensor for trimethylamine (TMA). The morphological and structural characterization of graphene/polystyrene-sulfonate nanocomposite were carried out by using Fourier-Transform infrared (FT-IR) spectroscopy, Raman spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy and field-effect scanning electron (FE-SEM) microscope. While, electrical conductivity was measured using a four-point probe measurement. The prepared polymer nanocomposite has a percolation threshold around 0.30% vol. fraction, with a conductivity of 2.45 S/m (rsd = 3.0%, n=3). The response of the composite sensor exhibited linear range from 23 to 183 mg/L (r2=0.95713) and the sensitivity was at 1.72 × 10-3 ΔR/R mg L-1. The gas sensor exhibited repeatable response to TMA gas and the calculated limit of detection was at 22.67 mg/L.