A New Microfluidics-Based Droplet Dispenser for ICPMS

Abstract

In this work, a novel droplet microfluidic sample introduction system for inductively coupled plasma mass spectrometry (ICPMS) is proposed and characterized. The cheap and disposable microfluidic chip generates droplets of an aqueous sample in a stream of perfluorohexane (PFH), which is also used to eject them as a liquid jet. The aqueous droplets remain intact during the ejection and can be transported into the ICP with >50% efficiency. The transport is realized via a custom-built system, which includes a membrane desolvator necessary for the PFH vapor removal. The introduction system presented here can generate highly monodisperse droplets in the size range of 40–60 μm at frequencies from 90 to 300 Hz. These droplets produced very stable signals with a relative standard deviation (RSD) comparable to the one achieved with a commercial droplet dispenser. Using the current system, samples with a total volume of <1 μL can be analyzed. Moreover, the capabilities of the setup for introduction and quantitative elemental analysis of single cells were described using a test system of bovine red blood cells. In the future, other modules of the modern microfludics can be integrated in the chip, such as on-chip sample pretreatment or parallel introduction of different samples.

A Microfluidic Chip for ICPMS Sample Introduction

“…Examples of a measurement of a standard solution and characterization of single cells are shown here. More examples can be found in Verboket et al 22 .…”

“…Use this detection efficiency to calculate the number of atoms in an unknown sample. NOTE: Since the variations between individual chips are small 22 , it is not necessary to repeat the measurement of the droplet size for every chip or solution if the flow rates remain the same. A list of the droplet sizes and frequencies according to the specific flow rates is published by Verboket et al 22 .…”

“…Recently, we introduced a microfluidic based system for sample introduction in ICPMS 22 . The key component of our introduction system is the liquid assisted droplet ejection (LADE) chip.…”

Current trends in single cell analysis

“…With this sample introduction method, metals in yeast cells have been detected already by Shigeta et al [9] at attogram levels. A similar approach was presented by Verboket et al [4], but they used a novel microfluidic system for droplet generation and direct injection into the ICP-MS. The core component of the system is based on liquid assisted droplet ejection (LADE) chip, which generates droplets in size ranges from 40 to 60 μm, in which single cells can be embedded in a highly volatile oil phase.…”

“…Microfluidic platforms routinely made of transparent materials such as polymers or glass are very well suited for microscopy and related techniques. In recent years, new interfaces have been developed to expand the analytical readout to the standard chemical methods, in particular mass spectrometry (e.g., Küster et al [3], Verboket et al [4]). …”