An approach to capillary electrophoresis with electrochemical detection (CE-EC) suitable for determination of dopamine in 1-min brain microdialysate samples is described. The CE-EC system includes an electrochemical detection cell that permits easy, precise, and permanent alignment of a carbon fiber microelectrode with a separation capillary (30-micron i.d., 75-cm length). Amperometric detection was performed at a constant applied potential of 600 mV with respect to a Ag/AgCl reference electrode. Decoupling of the electrophoretic current from the amperometric detector was accomplished with an integrated end-column decoupler prepared by etching the capillary outlet with HF. The decoupler produces baseline noise of 50 fA, or less, in the presence of 10-20-muA current in the separation capillary. The low baseline noise affords low mass (attomoles) and low concentration (nanomolar) detection limits for dopamine and 4-methylcatechol. A peak attributable to dopamine was identified in electropherograms of brain microdialysate samples obtained from anesthetized rats. Identification of the dopamine peak was confirmed by pharmacological methods. Dopamine was readily detected in 1-min brain microdialysate samples. The dopamine concentration in 1-min brain microdialysis samples was significantly altered by drug treatments and by brief electrical stimulation of dopaminergic axons.
An effective approach is required to pattern graphene with high spatial resolution and accuracy for advanced graphene-based sensors. In this work, we describe a simple and effective strategy for direct writing micro-scale graphene patterns by drop-ondemand (DoD) electrohydrodynamic jet (E-Jet) printing, using a highly concentrated graphene dispersion. The uniform micro-scale graphene patterns were formed by droplets produced under the electric field "pulling" force, these droplets are far smaller than the inner diameter of nozzle, which can effectively avoid nozzle clogging. With the control of pulse voltage width and frequency, different micro-scale graphene patterns were directly printed using DoD E-Jet printing technique. Graphene lines with a thickness of 5 nm were produced for 1 time printing, which provided a resistivity of 4.2 mΩ•cm. In addition, the graphene layer was directly written on the Pt microelectrodes to form Graphene/Pt (G/Pt) composite microelectrodes. The electrochemical test shows that the peak current of G/Pt composite microelectrodes was more than twice larger than that of bare Pt microelectrodes. The sensing sensitivity was significantly increased, presenting great potential for high performance electrochemical sensing devices.
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