Browsing by Author "Lu, Weihao"
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Item Determination of β-estradiol by surface-enhance raman spectroscopy (SERS) using a surface imprinted methacrylate polymer on nanoporous biogenic silica(2021) Mugo, Samuel; Lu, WeihaoA phytoplankton derived nanoporous biogenic silica (BS) scaffold grafted with polymethacrylate β-estradiol molecularly imprinted polymers (MIP) film (MIP@BS) is reported as a selective platform for the determination of β-estradiol using surfaced-enhanced Raman scattering (SERS). The biogenic silica nanoparticles provided high surface area support for the MIP while serving as an active signal enhancement substrate for SERS. The MIP@BS platform demonstrated an excellent linear response (R2 = 0.9996) between 0.1 and 4 ng/mL of β-estradiol standards. The limit of detection (LOD) for the MIP@BS SERS sensor for β-estradiol was 0.073 ng/mL. The MIP@BS SERS sensors were successfully evaluated for the determination of β-estradiol in milk, while demonstrating good stability and reusability.Item Modified stainless steel microneedle electrode for polyphenolics detection(2020) Dhanjai; Mugo, Samuel; Lu, WeihaoThis work outlines a simple fabricated microneedle electrode for sensitive and real sample monitoring of plant polyphenolics. The electrode was fabricated by layer-by-layer assembly (LBL) with nanocomposite of carbon nanotubes (CNT) and cellulose nanocrystals (CNC) as the first layer, followed by polyaniline (PANI), and finally, the 3-(glycidyloxypropyl) trimethoxysilane (GOPS) layer as the binding agent. The microneedle electrodes were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The developed microneedle electrodes were successfully applied for the capacitive detection of gallic acid (GA) and chlorogenic acid (CA) as polyphenol model compounds. The microneedle electrode was also used to quantify polyphenols in orange juice. The electrochemical capacitance responses were linearly proportional to the concentrations of GA and CA in the range of 0.1–87.23 μg/mL for GA and 0.1–78.01 μg/mL for CA. The calculated detection limits (LOD) for GA and CA were found to be 0.29 ± 0.2 μg/mL and 0.34 ± 0.2 μg/mL respectively. As minimally invasive technology, microneedle electrodes were found to be promising for successful in situ screening of antioxidants in different fruit matrices. The microneedle electrodes were also applied to the depth profiling of antioxidant content in fruit samples.Item A pathogen imprinted hybrid polymer capacitive sensor for selective Escherichia coli detection(2020) Mugo, Samuel; Lu, Weihao; Dhanjai, DhanjaiA versatile pathogen imprinted polymer electrochemical sensor has been developed for Escherichia coli detection. The sensor is based on layer by layer assembly of multi-walled carbon nanotubes (CNT), nanocellulose (CNC) films, integrated with polyaniline (PANI) doped phenylboronic acid (PBA). The sensing layer is a poly(methacrylic acid) based pathogen microcontact imprinted polymer (PIP). The PIP@PBA/PANI@CNT/CNC sensor exhibits a high affinity towards E. coli in real biological matrices, while effective in discriminating E. coli amidst other bacteria. Using capacitance and impedance as transduction methods, the PIP sensor recorded a low limit of E. coli detection of 8.7 ± 0.5 cfu/ml, with a rapid response of ≤5 min.Item Stainless steel electrochemical capacitive microneedle sensors for multiplexed simultaneous measurement of pH, nitrates, and phosphates(2022) Mugo, Samuel; Lu, Weihao; Lemieux, StephaneConcerns for agri-food safety and environmental management require development of simple to use and cost- and time effective multiplex sensors for point-of-need (PON) chemical analytics by public end-user. Simultaneous detection of nitrates, phosphates, and pH is of importance in soil and water analysis, agriculture, and food quality assessment. This article demonstrates a suite of stainless steel microneedle electrochemical sensors for multiplexed measurement of pH, nitrate, and phosphate using faradaic capacitance derived from cyclic voltammetry as the mode of detection. The multi-target microneedle sensors were fabricated by layer-by-layer (LbL) assembly in a stainless steel hypodermic microneedle substrate. For nitrate sensing, the stainless steel was coated with carbon nanotube/cellulose nanocrystal (CNT)/CNC) decorated with silver nanoparticles (Ag). For pH measurement, the polyaniline (pANI) was coated onto the CNT/CNC@Ag film, while for phosphate detection, the CNT/CNC/Ag @pANI microneedle was further decorated with ammonium molybdenum tetrahydrate (AMT). The microelectrode platforms were characterized by FTIR, Raman, and microscopic techniques. The nitrate- and phosphate-based microneedle electrochemical sensors had excellent selectivity and sensitivity, with a determined limit of detection (LOD) of 0.008 mM and 0.007 mM, respectively. The pH microneedle sensor was responsive to pH in the linear range of 3–10. The three microneedle sensors yielded repeatable results, with a precision ranging from 4.0 to 7.5% RSD over the concentration ranges tested. The inexpensive (~ 1 $ CAD) microneedle sensors were successfully verified for use in quantification of nitrate, pH, and phosphate in brewed black coffee as a real sample. As such, the microneedle sensors are economical devices and show great promise as robust platforms for PON precision chemical analytics.Item Wearable microneedle dual electrochemical sensor forsimultaneous pH and cortisol detection in sweat(2021) Mugo, Samuel; Lu, Weihao; Wood, Marika; Lemieux, StephaneWe report herewith an inexpensive flexible dual target electrochemical sensor for simultaneous detection of pH and cortisol in human sweat. The sensor was fabricated by printing layer by layer (LbL) on a conductive microneedle polydimethylsiloxane (PDMS) flexible substrate. The dual sensor integrates two detection chambers comprising polyaniline (PANi) and cortisol imprinted poly (glycidylmethacrylate-co ethylene glycol dimethacrylate) (poly (GMA-co-EGDMA)). The dual wearable sensor rapidly (< 1 min) responded linearly to pH in the range of 3–9, while the cortisol sensor chamber had a linear range of 0–100 ng/mL. The cortisol sensing region had an excellent limit of detection (LOD) of 1.4 ± 0.3 ng/mL, with intra-batch reproducibility of 2.4% relative standard deviation (%RSD). The inter-batch precision (%RSD for three different sensors) was determined to be 4.7%. Demonstrating excellent stability and reusability, a single patch of cortisol sensor was used for 15 times over a 30-day period, with minimal change in response. The dual analyte wearable sensors were effective for detection of pH and cortisol in real human sweat.