Browsing by Subject "Paper-based"

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Paper-based electrochemical platforms for separation, enrichment, and detection
(2017-05) Li, Xiang, Ph. D.; Crooks, Richard M. (Richard McConnell); Stevenson, Keith J.; Shear, Jason B.; Mullins, Charles B.; Werth, Charles J.
Paper based analytical devices (PADs) have great potential in the application of point-of-care diagnosis. This dissertation focuses on the design and application of PADs, especially ones that integrate with electrochemical systems, to tackle various problems in analytical chemistry, such as multi-analyte separation, sample enrichment, and sensitive detection. Four types of PADs are described in this dissertation. The first PAD (oPAD-Ep) is designed for multi-analyte separation. The oPAD-Ep is fabricated using the principle of origami to create a stack of connected paper layers as an electrophoresis channel. Due to the thinness of paper, a high electric field can be achieved with low voltage supply. Serum proteins can be separated and the device can be unfolded for post-analysis. The second PAD (oPAD-ITP) is designed on a similar principle as the oPAD-Ep, but it is applied for sample enrichment. The major modification is to adjust electrolyte conditions to enable isotachophoretic enrichment of analytes. DNA with various lengths can be enriched within a few minutes, and can be collected on one of the paper folds. The third PAD (hyPAD) also focuses on sample enrichment. The device is assembled with two different paper materials, nitrocellulose and cellulose. The hyPAD can perform faradaic ion concentration polarization experiments. This technique uses faradaic electrochemistry to create a local electric field gradient in the paper channel and can enrich charged analytes including: DNA, proteins, and nanoparticles. The fourth PAD (oSlip-DNA) focuses on sensitive electrochemical detection of DNA hybridization assays. This method integrates magnetic enrichment and electrochemical signal amplification via silver nanoparticles. Using voltammetry, sensitive detection of Hepatitis B Virus DNA is achieved on the low-cost device.
The development of a metalloimmunoassay for the detection of NT-proBNP
(2021-05-07) Pollok, Nicole Elise; Crooks, Richard M. (Richard McConnell); Richards, Ian; Schiavinato Eberlin, Livia; Anslyn, Eric V.; Hoffman, David
The purpose of this doctoral research is to develop a biosensor for the monitoring of heart failure (HF) in humans. Currently, there is no quantitative patient-facilitated method to monitor HF, and the physical symptoms that result are a poor representation of the acute state of the disease. The biomarker of interest is N-terminal prohormone brain natriuretic peptide (NT-proBNP) which is secreted from the cardiac muscle tissue when the heart is experiencing decompensation. The concentration of NT-proBNP has a direct correlation to the severity of HF, and it is used as the antigen in a metalloimmunoassay, where two monoclonal antibodies are used to sandwich NT-proBNP. One is conjugated to a magnetic microbead via a streptavidin-biotin interaction, and the other is conjugated to a 20 nm-diameter silver nanoparticle (AgNP) using a heterobifunctional cross-linker. The fully formed metalloimmunoassay is placed on a carbon screen-printed and Au electrodeposited sensing electrode to detect AgNP labels electrochemically. Ag charge collected from the assay is representative of the concentration of NT-proBNP in the sample. A phenomenon known as galvanic exchange (GE) is utilized in the detection of Ag. GE is a process that occurs when a zerovalent metal is immersed in a solution containing the oxidized form of a more noble metal. In this specific case, the exchange occurs between AgNP in the metalloimmunoassay and Au³⁺ generated on the sensing electrode. GE occurs because the standard reduction potential of Ag⁺ is slightly lower than Au³⁺. Significant findings of this project reveal that GE between AgNP and Au³⁺ is a process that results in only a partial exchange of AgNP with the Au³⁺ under physiologic conditions. It has also been found that, implementing two subsequent Au³⁺ electrogeneration steps improve the Ag collection efficiency and the reproducibility. Additionally, using heterobifunctional cross-linkers to covalently attach antibodies to AgNP and silver nanocubes (AgNCs) results in a lower limit of detection. These findings have led to the detection of NT-proBNP in buffer within clinically relevant ranges of 0.06-3.49 nM.