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Abstract
Carbon fiber nanotip electrodes (CFNEs) are essential for electrochemical recordings of neurotransmitter release in confined spaces like synapses and for intracellular measurements through cytoplasm insertion. However, fabricating CFNEs with small surface areas to reduce noise remains challenging. Conventional methods struggle in controlling electrode tip size and length, reproducibility and success rate of fabrication. Here, we established a reliable, straightforward and user-friendly method to fabricate and shape CFNEs, enabling control over tip diameter, length, and tailor tip geometry. This method utilizes real-time microscopy imaging for positioning cylindrical carbon fiber microelectrodes (CFMEs) into a potassium hydroxide droplet, where a series of time- and voltage- controlled pulses enables a gentle, stepwise electrochemical etching of the CFME tips. The microscope-guided electrode positioning determines the etched region, while voltage pulse size and number control the extent of CFME tip removal. Hence, real-time adjustments to electrode positioning at the droplet’s liquid-air interface and incremental voltage pulses enable precise electrode sculpturing, akin to woodcarving with a knife. Using this method, we demonstrate the successful fabrication of short (10 μm) CFNEs with tip diameters of ~100 nm and sculptured into two distinct geometries: cone and needle shaped electrodes. These CFNEs exhibited excellent electrochemical properties and were employed for low-current noise electroanalysis of dopamine (DA) released from individual ~200 nm liposomes preloaded with DA. The data, supported by in silico simulation, suggest that electrode shape influences detection efficiency of liposome sub-populations based on their size, thus highlighting the critical role of electrode geometry in vesicle-based electroanalysis studies.
Supplementary materials
Title
Supplementary information to "Electrochemical Droplet Sculpturing of Short Carbon Fiber Nanotip Electrodes for Neurotransmitter Detection"
Description
Supporting Data: Additional data include evaluation of etching efficiency for nanotip electrode fabrication under various conditions (Figure S1), a comparison of electrochemical properties between nanotip electrodes and 30 μm disk electrodes (Figure S2), size distribution of 200 mM DA-loaded liposomes along with a summary of all liposome size measurements (Figure S3), in silico simulation of current spikes generated from oxidation of DA release from single DA-loaded liposome rupturing at the nanotip electrode surface (Figure S4), an illustration of the pulse generator used in this study (Figure S5), and a summary of kinetic details for single spikes burst measured by needle-shaped and cone-shaped nanotip electrodes (Table S1).
Video 1: Fabrication of needle-shaped carbon fiber nanotip electrode
Video 2: Fabrication of cone-shaped carbon fiber nanotip electrode
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Title
Video 1: Fabrication of needle-shaped carbon fiber nanotip electrode
Description
This video illustrates the real-time fabrication of needle-shaped CFNE using the electrochemical droplet sculpturing method. By placing a CFME into a KOH droplet and positioning the glass-carbon interface near the air-water interface of the droplet, individual 200 ms voltage pulses are used to controllably etch the CFME into a needle-shaped CFNE.
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Title
Video 2: Fabrication of cone-shaped carbon fiber nanotip electrode
Description
This video illustrates the real-time fabrication of needle-shaped CFNE using the electrochemical droplet sculpturing method. By inserting a CFME into a KOH droplet and positioning the carbon fiber at partial distance into the droplet and applying individual 200 ms voltage pulses a cone-shaped CFNE is fabricated.
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