A Tunable Three-Dimensional Printed Microfluidic Resistive Pulse Sensor for the Characterization of Algae and Microplastics

Abstract

Technologies that can detect and characterise particulates in liquids have applications in health, food and environmental monitoring. Simply counting the numbers of cells or particles however is not sufficient for most applications, and other physical properties must also be measured. Typically, it is necessary to compromise between chemical and biological specificity of the sensor and its speed. Here we present a low-cost and high-throughput multiuse counter that classifies a particle's size, concentration, porosity and shape. Using an additive manufacturing process, we have assembled a reusable flow resistive pulse sensor capable of being be tuned in real time to measure particles from 2-30 m, across a range of salt concentrations i.e. 2.5 × 10-4 to 0.1M. The device remains stable for several days with repeat measurements. We demonstrate its use for characterising algae with spherical and rod structures as well as microplastics shed from teabags. We present a methodology that results in a specific signal for microplastics, namely a conductive pulse, in contrast to particles with smooth surfaces such as calibration particles or algae, allowing the presence of microplastics to be easily confirmed and quantified. In addition, the shape of the signal and particle are correlated, giving an extra physical property to characterise suspended particulates. The technology can rapidly screen volumes of liquid, 1 mL/ min, for the presence of microplastics and algae.

Universal Nanopore Platform Integrating Multiple Resistive Pulse Sensors into a Single Microfluidic Device

“…The concept involves using our previously published AM tuneable flow device 15 as a core, referred to here as the "fluidic chip". Exploiting the fluidic chip as the central part to build upon allowed other electrodes and RPS sensors to be added (figure 2).…”

“…Increasingly known as resistive pulse sensing/ sensors (RPS), devices based on this principle have now been created from a range of materials from graphene, [1][2][3] to polymers, 4,5 silicon nitride 6 and glass. [7][8][9][10][11] The sensing process is simple, by monitoring the temporary changes in current caused by the translocation of an analyte through a narrow constriction, termed a sensing region or pore, RPS can characterise analytes according to size, 12 concentration, 13 shape [14][15][16][17] and charge. 18 The transport of an analyte through the pore is controlled by tuning the applied electric field, charge on the pore wall, electrophoretic mobility of the analyte, supporting electrolyte concentration and induced convection.…”

“…41 In a subsequent design, we extended the sensing dynamic range down to 5 m using a re-sealable lid and tuneable PDMS gasket layer. 15 However, this was insufficient to study nanomaterials.…”

Biochip with multi-planar electrodes geometry for differentiation of non-spherical bioparticles in a microchannel

“…Maugi et al, designed a microfluidic sensor to detect particles below 5 μm while using polyurethane (PU) nanopores to identify the shape of individual nanoparticles in solution. However, nanorods with an aspect ratio less than 2 are indistinguishable from nanospheres in this setup 34 , 35 . Pollard et al fabricated an RPS chip using additive manufacturing (AM) method with pores of 40 µm in diameter.…”

“…Pollard et al fabricated an RPS chip using additive manufacturing (AM) method with pores of 40 µm in diameter. The pulse shape shown was the characteristic of the channel dimensions 35 . Although, these findings are encouraging, the requirement that pore sizes must be close to the particles’ size being studied has disadvantages.…”