Fabrication of inexpensive and flexible electronic and electrochemical sensors is in high demand for a wide range of biochemical and biomedical applications. We explore hand fabrication of CNT modified AgNPs electrodes using wax-on-plastic platforms and their application in electrochemical immunosensing. Wax patterns were printed on polyethylene terephthalate-based substrates to laydown templates for the electrodes. Hand painting was employed to fabricate a silver conductive layer using AgNPs ink applied in the hydrophilic regions of the substrate surrounded by wax. CNT was drop cast on top of the working electrodes to improve their electrochemical signal. The device layers were characterized by scanning electron microscopy. The electrochemical performance of the hand fabricated AgNPs and CNT/AgNPs electrodes was tested using cyclic voltammetry, differential pulse voltammetry, and amperometry. The electrochemical response of CNT/AgNPs electrodes was relatively faster, higher, and more selective than unmodified AgNPs sensing electrodes. Finally, the hand-painted CNT/AgNPs electrodes were applied to detect carcinoembryonic antigen (CEA) by measuring the end-product of immunoassay performed on magnetic particles. The detection limit for CEA was found to be 0.46 ng/mL.
Flexible and ultrasensitive biosensing
platforms capable of detecting
a large number of trinucleotide repeats (TNRs) are crucial for future
technology development needed to combat a variety of genetic disorders.
For example, trinucleotide CGG repeat expansions in the FMR1 gene can cause Fragile X syndrome (FXS) and Fragile X-associated
tremor/ataxia syndrome (FXTAS). Current state-of-the-art technologies
to detect repeat sequences are expensive, while relying on complicated
procedures, and prone to false negatives. We reasoned that two-dimensional
(2D) molybdenum sulfide (MoS2) surfaces may be useful for
label-free electrochemical detection of CGG repeats due to its high
affinity for guanine bases. Here, we developed a low-cost and sensitive
wax-on-plastic electrochemical sensor using 2D MoS2 ink
for the detection of CGG repeats. The ink containing few-layered MoS2 nanosheets was prepared and characterized using optical,
electrical, electrochemical, and electron microscopic methods. The
devices were characterized by electron microscopic and electrochemical
methods. Repetitive CGG DNA was adsorbed on a MoS2 surface
in a high cationic strength environment and the electrocatalytic current
of the CGG/MoS2 interface was recorded using a soluble
Fe(CN)6
–3/–4 redox probe by differential
pulse voltammetry (DPV). The dynamic range for the detection of prehybridized
duplexes ranged from 1 aM to 100 nM with a 3.0 aM limit of detection.
A detection range of 100 fM to 1 nM was recorded for surface hybridization
events. Using this method, we were able to observe selectivity of
MoS2 for CGG repeats and distinguish nonpathogenic from
disease-associated repeat lengths. The detection of CGG repeat sequences
on inkjet printable 2D MoS2 surfaces is a forward step
toward developing chip-based rapid and label-free sensors for the
detection of repeat expansion sequences.
Bioelectronic devices that interface electronics with biological systems can actuate and control biological processes. The potassium ion plays a vital role in cell membrane physiology, maintaining the cell membrane potential (Vmem) and generating action potentials. In this work, we present two bioelectronic ion pumps that use an electronic signal to modulate the potassium ion concentration in solution. The first ion pump is designed to integrate directly with six-well cell culture plates for optimal ease of integration with in vitro cell culture, and the second on-chip ion pump provides high spatial resolution. These pumps offer increased ease of integration with in vitro systems and demonstrate K+ concentration distribution with high spatial resolution. We systematically investigate the ion pump’s performance using electrical characterization and computational modeling, and we explore closed-loop control of K+ concentration using fluorescent dyes as indicators. As a proof-of-concept, we study the effects of modulating K+ concentration on Vmem of THP-1 macrophages.
The sequence-dependent properties of the surface-assembled trinucleotide repeat interface on a gold surface were explored by electrochemical methods and surface probe microscopy.
DNA is strongly adsorbed on oxidized graphene surfaces in the presence of divalent cations. Here, we studied the effect of DNA adsorption on electrochemical charge transfer at few-layered, oxygen-functionalized graphene (GOx) electrodes. DNA adsorption on the inkjet-printed GOx electrodes caused amplified current response from ferro/ferricyanide redox probe at concentration range 1 aM–10 nM in differential pulse voltammetry. We studied a number of variables that may affect the current response of the interface: sequence type, conformation, concentration, length, and ionic strength. Later, we showed a proof-of-concept DNA biosensing application, which is free from chemical immobilization of the probe and sensitive at attomolar concentration regime. We propose that GOx electrodes promise a low-cost solution to fabricate a highly sensitive platform for label-free and chemisorption-free DNA biosensing.
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