Discipline: Chemistry and Chemical Sciences
Xaimara Santiago Maldonado - University of Puerto Rico Rio Piedras
Co-Author(s): Agnes M. Ríos-Delgado, University of Puerto Rico, Rio Piedras Campus, San Juan, PR; Eduardo Nicolau-López, University of Puerto Rico, Rio Piedras Campus, San Juan, PR
N-methylamino-l-alanine (L-BMAA) is a neurotoxic cyanotoxin that has been linked to an elevated incidence of neurodegenerative diseases. It is produced by a diverse range of cyanobacteria in different environments. Climate change and anthropogenic sources, like high water temperatures and oversupply of nutrients, causes an increment of size and frequency of cyanobacterial blooms and consequently, increases the concentration of cyanotoxins like L-BMAA. This cyanotoxin is difficult to measure in water because of its high hydrophilicity, no fluorescent or ultraviolet characteristics, and the presence of isomers that may cause false positives and hinder the separation processes. Therefore, the development of analytical techniques for specific and sensitive detection of this toxin is imperative. In this work, we propose the development of an impedimetric biosensor combining the superior target recognition capabilities of aptamers with the mass transfer advantages of cylindrical nanopores that are formed by the diblock-copolymer polystyrene-poly(methylmethacrylate) (PS-b-PMMA). Coated electrodes with block-copolymers (BCP’s) lead to the formation of recessed nanodisk-array electrodes (RNEs) that provide primary mass transport pathways for ionic and redox active species which changes upon analyte binding. Our hypothesis is that the development of an impedimetric biosensor combining a highly specific aptamer with the RNEs will lead to the advancement of an innovative aptasensor for a sensitive, portable, economic and flexible way to achieve the detection of L-BMAA in water. The nanoporous electrodes, are fabricated with a PS-b-PMMA solution in toluene deposited over gold-coated silicon wafers via spin coating and followed by annealing and UV etching. Different annealing times, temperatures and UV exposure has been accomplished in order to produce the alignment of the cylindrical polymer microdomains in a vertical fashion over the surface of the electrode. The prepared films are characterized by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to confirm the formation of recessed nanodisk-array electrodes. CV data shows sigmoidal curves at high scan rates characteristic of recessed nanodisk-array electrodes, suggesting the formation of this type of nanopores with a sufficiently large distance among them to attain radial diffusion. Atomic force microscopy (AFM) images of the samples evidence the formation of vertical nanopores with mixed horizontal alignments. Moreover, grazing incident small angle x-ray scattering (GISAXS) suggests that the polymer was well-dispersed among the surface although the expected scattering profile for RNEs is missing. Future work includes the optimization of the electrode preparation methods and the selection of a L-BMAA specific aptamer through graphene oxide-assisted selection evolution of ligands by exponential enrichment (GO-SELEX).
Funder Acknowledgement(s): We would like to acknowledge the CREST Center for Innovation, Research, and Education in Environmental Nanotechnology (CIRE2N). This program is funded by National Science Foundation, HRD #1736093 and University of Puerto Rico, R?o Piedras Campus.
Faculty Advisor: Dr. Eduardo Nicolau, email@example.com
Role: I work on both the electrode preparation using block-copolymer and the aptamer selection for the biosensor. I also perform the electrochemical and surface analysis characterization except for the GISAXS analysis.