In this work, different paper surface modification strategies were compared to obtain an amine functionalized SBA-15 (N-SBA-15) composite for paper-based device development. The synthesized N-SBA-15 was characterized by N 2 adsorption-desorption isotherm, and infrared spectroscopy (FTIR), and it was incorporated to different polymer matrices (κ-carrageenan (CA), polyvinyl alcohol (PVA) and polyethylenimine (PEI)) for the development of the composite modified paper-based device. The retention, interactions, and morphology of the obtained composites were investigated by absorbance measurement, 2 FTIR and scanning electron microscopy (SEM), respectively. To demonstrate the applicability of the modified paper-based device, ascorbic acid (AA) quantification was carried out. Horseradish peroxidase (HRP) was immobilized onto the modified paper surface. HRP in the presence of H 2 O 2 catalyzes the oxidation of 10-acetyl-3,7dyhidroxyphenoxazine (ADHP) to highly fluorescent resorufin, which was measured by LIF detector. Thus, when AA was added to the solution, it decreases the relative fluorescence signal proportionally to the AA concentration. The linear range from 50 nmol L-1 to 1500 nmol L-1 and a detection limit of 15 nmol L-1 were obtained for AA quantitation. The obtained results allowed us to conclude that N-SBA-15/PEI composite could be considered an excellent choice for the paper-based device modification procedure due to its inherent simplicity, low cost, and sensitivity.
A novel fluorescent paper based immunosensor for the quantification of gliadin content in different food samples was constructed. The device consists of a paper platform modified with amino functionalized mesoporous material. The nanoporous structure and the aminofunctionality increased the anti-gliadin antibodies immobilization capacity of the sensing surface, conferring high sensitivity to the system. The detection limit reached by the described system allowed us to address the control of gluten free foods, which is extremely important to maintain the food safe consumption by patients with celiac disease, wheat allergy measured by immunoglobulin E, non-celiac gluten intolerance and Dermatitis herpetiformis or Duhring disease. The gliadin determination was performed by applying a noncompetitive immunoassay format, where gliadin present in food samples was recognized by anti-gliadin antibodies immobilized on the mesoporous material and quantified by the addition of anti-gliadin antibody labelled with peroxidase, its substrate: hydrogen peroxide and a mediator: 10-acetyl-3,7-dihydrofenoxacin. This mediator by the action of the enzyme generates resorufin, which was excited by a light emitting diode at 550 nm and emitted a signal at 580nm. The calibration curve obtained for gliadin exhibited a linear range between 0-160 µg Kg-1 and a method detection limit of 0.025 mg Kg-1. The obtained values for relative recovery varied between 98.65% and 102.33% for samples enriched with gliadin. Also, the results suggested that the developed fluorescent paper based immunosensor showed good reproducibility and stability, indicating its applicability for high-sensitive gluten free food control analysis.
In this work, a novel paper-based analytical device (PAD) coupled with LED-induced fluorescence (LIF) detection (fPAD) for the rapid, selective, and sensitive quantification of phenylalanine (Phe) in neonatal samples was developed.
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