Centrifugal Step Emulsification: How Buoyancy Enables High Generation Rates of Monodisperse Droplets

Abstract

We demonstrate that buoyancy in centrifugal step emulsification enables substantially higher generation rates of monodisperse droplets compared to pressure driven set-ups. Step emulsification in general can produce droplets in comparatively simple systems (only one moving liquid) with a low CV of <5% in droplet diameter and with a minimum dead volume. If operated below a critical capillary number, the droplet diameter is defined by geometry and surface forces only. Above that critical capillary number, however, jetting occurs, leading to an increased droplet diameter and CV. Consequently, generation rates of monodisperse droplets are limited in pressure-driven systems. In this paper, we show that centrifugal step emulsification can overcome this limitation by applying sufficient buoyancy to the system. The buoyancy, induced by the centrifugal field and a density difference of the continuous and disperse phase, supports droplet necking by pulling the forming droplet away from the nozzle. The influence of buoyancy is studied using specific microfluidic designs that allow for supplying different buoyancies to the same droplet generation rates. For a droplet diameter of 100 μm, droplet generation at rates above 2.8k droplets per second and nozzle were reached, which is an increase of more than a factor of 8 in comparison to pressure-driven systems.

Point-of-Care System for HTLV-1 Proviral Load Quantification by Digital Mediator Displacement LAMP

“…An elevated rotational frequency allows the liquid to be transported into the detection chambers. Centrifugal step emulsification [30] generates droplets with a diameter of 100 µm (Figure 2j). A stroboscopic image of the droplet generation is depicted in the ESI in Figure S4.…”

“…According to the variance given in the literature, the theoretical number of nucleic acid copies per MT-2 cell is highlighted as a grey area ranging from 1 to 16 copies per MT-2 cell (Figure 3). To determine the number of HTLV-1 copies per MT-2 cell, we conducted a dLAMP of HTLV-1 with fresh reagents on a microfluidic chip ( Figure S6) as described previously [30]. Zero, 21, 210, and 2100 MT-2 cells per assay were extracted manually with MagaZorb DNA Mini-Prep Kit.…”

Versatile Tool for Droplet Generation in Standard Reaction Tubes by Centrifugal Step Emulsification

“…The workflow for emulsification can be described as follows (see Figure 1a): The cartridge is placed into a 2 mL reaction tube and both fluorinated oil and the aqueous sample is pipetted into the particular inlets. After closing the lid to prevent evaporation and contamination, the tube is inserted into a standard laboratory centrifuge for droplet generation by centrifugal step emulsification [14,16]. After processing at a fixed centrifugal acceleration of 80 g (calculated for the rcf reference point; see Figure 1b (viii)), the cartridge is removed from the tube and the generated emulsion is ready for follow-up steps such as incubation or, transfer to other devices.…”

“…The fields of application range from DNA and RNA analysis [1][2][3][4] to applications in the chemical-, medical-, cosmetic-, or food-industry [5][6][7][8]. For the processing of monodisperse droplets, the existing microfluidic technologies can be classified into two general categories: (i) On-chip systems, where the droplets remain in the cartridge and analysis and droplet manipulation are performed on-chip [9][10][11][12][13][14][15][16]. (ii) Off-chip systems, where the droplets are transferred into a reaction tube and downstream analysis and/or further manipulation steps are performed in bulk [4,[17][18][19][20].…”

“…In this work, we present an off-chip system that uses centrifugal step emulsification [12,16] to generate aqueous droplets in fluorinated oil. The cartridge is manufactured out of two parts, one monolithic fluidic layer and a sealing foil and can be processed in 2 mL reaction tubes on standard centrifuges.…”