1-Octanol-assisted ultra-small volume droplet microfluidics with nanoelectrospray ionization mass spectrometry

• Published in: Analytica chimica acta 2024-09, Vol.1321, p.342998, Article 342998
• Main Authors: Zhao, Yaoyao, Park, Insu, Rubakhin, Stanislav S., Bashir, Rashid, Vlasov, Yurii, Sweedler, Jonathan V.
• Format: Article
• Language: English
• Subjects: 1-Octanol - chemistry; Acetylcholine - analysis; Animals; Cerebral spinal fluid; Droplet microfluidics; gamma-Aminobutyric Acid - analysis; Lab-On-A-Chip Devices; Low volume sampling; Mass spectrometry; Microfluidic Analytical Techniques - instrumentation; Nanotechnology; Neurotransmitters; Particle Size; Rats; Spectrometry, Mass, Electrospray Ionization - methods
• ISSN: 0003-2670; 1873-4324; 1873-4324
• DOI: 10.1016/j.aca.2024.342998

Droplet microfluidics with push-pull and microdialysis sampling from brain slices, cultured cells and engineered tissues produce low volume mass limited samples containing analytes sampled from the extracellular space. This sampling approach coupled to mass spectrometry (MS) detection allows evaluation of time-dependent chemical changes. Our goal is an approach for continuous sampling and segregation of extracellular samples into picoliter droplets followed by the characterization of the droplets using nanoelectrospray ionization (nESI) MS. The main focus here is the optimization of the carrier oil for the microfluidic device that neither affects the stability of picoliter droplets nor compatibility with MS detection of a range of analytes. We developed and characterized a 1-octanol-assisted ultra-small volume droplet microfluidic nESI MS system for the analysis of neurotransmitters in distinct samples including cerebrospinal fluid (CSF). The use of a 1-octanol oil phase was effective for generation of aqueous droplets as small as 65 pL and enabled detection of acetylcholine (ACh) and gamma-aminobutyric acid (GABA) in water and artificial CSF. Continuous MS analysis of droplets for extended periods up to 220 min validated the long-term stability of droplet generation and analyte detection by nESI-MS. As an example, ACh response demonstrated a linear working range (R2 = 0.99) between 0.4 μM and 25 μM with a limit of detection of 370 nM (24 amol), enabling its quantitation in rodent CSF. The established droplet microfluidics – nESI MS approach allows the analysis of microenvironments at high spatiotemporal resolution. The approach may allow microsampling and monitoring of spatiotemporal dynamics of neurochemicals and drugs in the brain and spinal cord of live animals. [Display omitted] •A pL droplet microfluidic-nESI MS system optimized for neurotransmitter detection.•The 1-octanol oil phase effectively generates aqueous droplets as small as 65 pL.•Long-term stability for droplet generation and analyte detection by MS.•Acetylcholine quantified from rat cerebral spinal fluid samples.•Characteristics of the system designed for in vivo monitoring of neurotransmitters.