Label-free oligonucleotide sensors that use a change in the electrode kinetics of the redox reaction of the negatively charged Fe(CN)(6)(3-/4-) redox couple to signal the formation of a DNA duplex with a surface-conjugated probe nucleotide are investigated. Electrochemically active conducting polymers (ECPs) can advantageously be used both as the active electrode and as the means of surface conjugation of the probe nucleotide. Here, we demonstrate that the sensitivity of the detection of the surface-complementary oligonucleotide can significantly be improved, into the low nanomolar range, by forming the ECP as a highly porous, very rough layer by growing it using electrochemical polymerization on a microelectrode. In comparison, smoother surfaces formed on macroelectrodes had detection sensitivity in the low micromolar range. We propose Donnan exclusion of the redox couple from small pores as the reason for the enhanced sensitivity. We discuss the effects using a simple patch model for the electrochemical kinetics and use the model to derive the equilibrium binding constant and binding kinetic rate constants for the surface hybridization reaction. We use the electrochemically active copolymer of pyrrole (Py) and 3-pyrrolylacrylic acid (PAA) [poly(Py-co-PAA)] as the sensing electrode and binding surface and measure the surface hybridization-induced changes in electrode kinetics of Fe(CN)(6)(3-/4-) by electrochemical impedance spectroscopy.
Developing tools
that are able to monitor transient neurochemical
dynamics is important to decipher brain chemistry and function. Multifunctional
polymer-based fibers have been recently applied to monitor and modulate
neural activity. Here, we explore the potential of polymer fibers
comprising six graphite-doped electrodes and two microfluidic channels
within a flexible polycarbonate body as a platform for sensing pH
and neurometabolic lactate. Electrodes were made into potentiometric
sensors (responsive to pH) or amperometric sensors (lactate biosensors).
The growth of an iridium oxide layer made the fiber electrodes responsive
to pH in a physiologically relevant range. Lactate biosensors were
fabricated via platinum black growth on the fiber electrode, followed
by an enzyme layer, making them responsive to lactate concentration.
Lactate fiber biosensors detected transient neurometabolic lactate
changes in an in vivo mouse model. Lactate concentration changes were
associated with spreading depolarizations, known to be detrimental
to the injured brain. Induced waves were identified by a signature
lactate concentration change profile and measured as having a speed
of ∼2.7 mm/min (
n
= 4 waves). Our work highlights
the potential applications of fiber-based biosensors for direct monitoring
of brain metabolites in the context of injury.
In this communication, al abel-freea nd sensitive electrochemical method to detectp otassium ions is proposed. The conducting polymer polypyrrole was used as both an anchor for the probe and at ransducer of the detection event.AK + -specific G-rich aptamer was applied asarecognition element, which folded into the G-quadruplex structure in the presence of K + ,a nd this resulted in an increase in the electrode impedance. The combination of the K + -selective aptamer and the porous conducting polymer as as ignal transducer afforded as uccessful sensorp latform. The sensor responded approximately logarithmically over aw ide dynamic range of K + concentrationsf rom 20 fm to 1mm,w ith av ery low detection limit of 14.7 fm and excellent discrimination against other ions. Additionally,e lectrochemicali mpedance spectroscopy was used to study the kinetics of K + bindinga tt he conducting polymer-immobilized aptamers urface, whichi ndicated strong binding between the two. This work demonstrates ap owerful approach for the sensitive, selective, and direct electrochemical detection of metal ions based on the switching conformation of G-rich aptamers attachedt oap orous conducting polymer surface. This assay scheme can be expanded to the detection of aw ider ange of targets by modifying the aptamer structure as ar ecognizing moiety.
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