Biosensing extracellular vesicles: contribution of biomolecules in affinity-based methods for detection and isolation.

Extracellular Vesicles (EVs) are lipid vesicles secreted by cells that allow intercellular communication. They are decorated with surface proteins, which are membrane proteins that can be targeted by biochemical techniques to isolate EVs from background particles. EVs have recently attracted attention for their potential applications as biomarkers for numerous diseases. This review focuses on the contribution of biomolecules used as ligands in affinity-based biosensors for the detection and isolation of EVs. Capturing biological objects like EVs with antibodies is well described in the literature through different biosensing techniques. However, since handling proteins can be challenging due to stability issues, sensors using non-denaturable biomolecules are emerging. DNA aptamers, short DNA fragments that mimic antibody action, are currently being developed and considered as the future of antibody-like ligands. These molecules offer undeniable advantages: unparalleled ease of production, very high stability in air, similar affinity constants to antibodies, and compatibility with many organic solvents. The use of peptides specific to EVs is also an exciting biochemical solution to target EV membrane proteins and complement other probes. These different ligands have been used in several types of biosensors: electrochemical, optical, microfluidic using both generic probes (targeting widely expressed membrane proteins such as the tetraspanins) and specific probes (targeting disease biomarkers such as proteins overexpressed in cancer).

Continuous microcarrier-based cell culture in a benchtop microfluidic bioreactor.

Microfluidic bioreactors are expected to impact cell therapy and biopharmaceutical production due to their ability to control cellular microenvironments. This work presents a novel approach for continuous cell culture in a microfluidic system. Microcarriers (i.e., microbeads) are used as growth support for anchorage-dependent mammalian cells. This approach eases the manipulation of cells within the system and enables harmless extraction of cells. Moreover, the microbioreactor uses a perfusion function based on the biocompatible integration of a porous membrane to continuously feed the cells. The perfusion rate is optimized through simulations to provide a stable biochemical environment. Thermal management is also addressed to ensure a homogeneous bioreactor temperature. Eventually, incubator-free cell cultures of Drosophila S2 and PC3 cells are achieved over the course of a week using this bioreactor. In future applications, a more efficient alternative to harvesting cells from microcarriers is also anticipated as suggested by our positive results from the microcarrier digestion experiments.

Effect of substrate wettability in liquid dielectrophoresis (LDEP) based droplet generation: theoretical analysis and experimental confirmation.

The generation of droplets for biological reactions at the microscale can be achieved by many techniques, among which the so-called liquid dielectrophoresis technique (LDEP). This is not a new process, but the parameters influencing actuation voltage still need further insight: size and geometry (electrodes width and gap, dielectric thickness), materials (dielectric constant), liquids (surface tension, dielectric constant, conductivity), working conditions (voltage, frequency) and substrate wettability (contact angle). This large experimental space is firstly reduced using non dimensional numbers and then studied in a systematic way thanks to the design of experiments. The contact angle influence is explained thanks to a new analytical model. To summarize, this paper recalls analytical models used to predict the voltage threshold required to develop a liquid rivulet from a mother drop, taking the contact angle into account and providing a large set of experimental results.

An embedded microchannel in a MEMS plate resonator for ultrasensitive mass sensing in liquid.

A mass sensor innovative concept is presented here, based on a hollow plate Micro Electro Mechanical System (MEMS) resonator. This approach consists in running a solution through an embedded microchannel, while the plate resonator is actuated according to a Lamé-mode by electrostatic coupling in dry environment. The experimental results have shown a clear relationship between the measured shift of the resonance frequency and the sample solution density. Additionally, depending on the channel design and the solution properties, the quality factor (Q-factor) was noticed maintaining its level and even substantial improvement in particular cases. Resonators demonstrate resonance frequencies close to 78 MHz and Q-factor of a few thousands for liquid phase detection operating at ambient temperature and atmospheric pressure. Frequency fluctuations study revealed a 13 Hz instability level, equivalent to 1.5 fg in mass. Using a fully electronic readout configuration, a mass responsivity of ca. 850 fg kHz(-1) was monitored.