We present the fabrication of high-quality graphitic micro-wires in diamond which are conductive in nature using pulsed Bessel beams. The electrodes are created in the bulk of 500 μm thick monocrystalline CVD and HPHT diamond samples perpendicular to the sample surface without sample translation or beam scanning. The role of various beam parameters such as pulse energy and pulse duration, different crystallographic orientations of the sample and two different writing modes of the laser namely burst mode and single-pulse mode in the conductivity of such electrodes are investigated. While the morphology of the electrodes is analysed using optical microscopy, the conductivity is measured experimentally using current-voltage characterisation. Furthermore, micro-Raman spectroscopy is implemented to investigate the graphitic content of electrodes fabricated. We have observed that higher pulse duration favours better conductivity while pulse energy has an optimum value for the same. As for the crystallographic orientations, we have found that it is possible to eradicate the potential barrier in the current-voltage curves completely even for graphitic wires fabricated at low pulse energy and in the fs pulse duration regime in a (110) oriented sample in contrast to the (100) oriented-crystal case where the barrier is generally observed. Finally, in case of wires fabricated with laser bursts with femtosecond sub-pulses, the higher number of sub-pulses, lower time delay between them and longer total burst duration favours better conductivity. Through various optimisation techniques, we report resistivity values as low as 0.01 Ω cm for the Bessel beam written electrodes in diamond.
Dopamine (DA) is an important neurotransmitter in the human body, mainly in the brain. It plays a pivotal role in regulating various physiological functions such as mood regulations and it is crucial for reinforcing behaviors linked to pleasure and survival. Variation of its concentration is a reason for numerous neurological diseases such as Parkinson’s disease which makes its detection vital for early diagnosis and drug screening. Detecting dopamine, however, comes with its own set of challenges, particularly due to the necessity for methods that are highly sensitive and specific. This paper reports an improved method for the detection of exocytotic events from dopaminergic neurons by merging the electrochemical properties of the ion beam induced graphitic electrodes on diamond and the capabilities of a stereolithography (SLA) 3D printer to produce a droplet-based microfluidic biosensor.
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