One of the major challenges for in vivo electrochemical measurements of dopamine (DA) is to achieve selectivity in the presence of interferents, such as ascorbic acid (AA) and uric acid (UA). Complicated multimaterial structures and ill-defined pretreatments have been frequently utilized to enhance selectivity. The lack of control over the realized structures has prevented establishing associations between the achieved selectivity and the electrode structure. Owing to their easily tailorable structure, carbon nanofiber (CNF) electrodes have become promising materials for neurobiological applications. Here, a novel yet simple strategy to control the sensitivity and selectivity of CNF electrodes toward DA is reported. It consists of adjusting the lengths of CNF by modulating the growth phase during the fabrication process while keeping the surface chemistries similar. It was observed that the sensitivity of the CNF electrodes toward DA was enhanced with the increase in the fiber lengths. More importantly, the increase in the fiber length induced (i) an anodic shift in the DA oxidation peak and (ii) a cathodic shif t in the AA oxidation peak. As the UA oxidation peak remained unaffected at high anodic potentials, the electrodes with long CNFs showed excellent selectivity. Electrodes without proper fibers showed only a single broad peak in the solution of AA, DA, and UA, completely lacking the ability to discriminate DA. Hence, the simple strategy of controlling CNF length without the need to carry out any complex chemical treatments provides us a feasible and robust route to fabricate electrode materials for neurotransmitter detection with excellent sensitivity and selectivity.
Electrode fouling
is a major factor that compromises the performance
of biosensors in in vivo usage. It can be roughly
classified into (i) electrochemical fouling, caused by the analyte
and its reaction products, and (ii) biofouling, caused by proteins
and other species in the measurement environment. Here, we examined
the effect of electrochemical fouling [in phosphate buffer saline
(PBS)], biofouling [in cell-culture media (F12-K) with and without
proteins], and their combination on the redox reactions occurring
on carbon-based electrodes possessing distinct morphologies and surface
chemistry. The effect of biofouling on the electrochemistry of an
outer sphere redox probe, [Ru(NH3)6]3+, was negligible. On the other hand, fouling had a marked effect
on the electrochemistry of an inner sphere redox probe, dopamine (DA).
We observed that the surface geometry played a major role in the extent
of fouling. The effect of biofouling on DA electrochemistry was the
worst on planar pyrolytic carbon, whereas the multiwalled carbon nanotube/tetrahedral
amorphous carbon (MWCNT/ta-C), possessing spaghetti-like morphology,
and carbon nanofiber (CNF/ta-C) electrodes were much less seriously
affected. The blockage of the adsorption sites for DA by proteins
and other components of biological media and electrochemical fouling
components (byproducts of DA oxidation) caused rapid surface poisoning.
PBS washing for 10 consecutive cycles at 50 mV/s did not improve the
electrode performance, except for CNF/ta-C, which performed better
after PBS washing. Overall, this study emphasizes the combined effect
of biological and electrochemical fouling to be critical for the evaluation
of the functionality of a sensor. Thus, electrodes possessing composite
nanostructures showed less surface fouling in comparison to those
possessing planar geometry.
Tuning of the viscoelastic properties of supramolecular hydrogels to be used as biological material substrates in tissue engineering has become significantly relevant in recent years due to their ability to influence cell fate. In the quest to enhance the stability and mechanical properties of a derived C2-phenylalanine gelator (LPF), derivatives of the polysaccharide dextran were incorporated as additives to promote hydrogen bonding and π−π stacking with the gelator. Dextran was esterified to yield carboxymethyl dextran (CMDH), which was subsequently amidated to furnish amino dextran (AD), the resulting hybrid hydrogels were denoted as LPF-AD x and LPF-CMDH x , where x represents the amount of AD and CMDH (mg). The LPF gelator interacted with the carboxyl and amino functional groups of the CMDH and AD, respectively, through hydrogen bonding and π−π stacking, resulting in mechanically stable hydrogels. Morphological studies revealed that the hybrid hydrogels were formed as a result of dense highly branched thin and broad fibers for LPF-AD and LPF-CMDH, respectively. Rheological studies confirmed the superiority of the hybrid hydrogels over the neat hydrogel, where LPF-CMDH 3 exhibited the best mechanical properties with an improved elastic modulus of 11 654 Pa over 1518 and 140 Pa for LPF-AD 4.5 and LPF, respectively. The adhesion and spreading behavior of NIH 3T3 fibroblast cells were significantly improved on the LPF-CMDH 3 substrate owing to their enhanced mechanical properties. The tuning of the mechanical properties of the therein hydrogels via the facile incorporation of biodegradable and biocompatible functionalized additives opens up avenues for strengthening the supposed weak supramolecular gelators and hence increasing their potential of being employed largely in the field of tissue engineering.
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