The analysis of nanoparticles (NPs) in biological matrices poses many challenges when trying to sample specific particles. We explored various Lab-on-chip (LoC) filtering components, with a particular focus on Field-flow fractionation (FFF) coupled with 3D dynamic light scattering (DLS) to provide size-related information. The LoC allows us to work on a small scale and with small amounts of sample solvents.

At SDU-NanoSYD we want to optimize nanoparticle detection efficiency. The particles that we want to detect are in a food matrix or other matrix of solvents. For sensitive detection, it is crucial to extract the particles from the matrix and preferably sort them by size.

We explored Field-flow fractionation (FFF) coupled with 3D dynamic light scattering (DLS) to provide size related information. The NPs, to be detected from food or other matrices of solvents, are mechanically pre-filtered by commercial syringe filters. Afterwards, based on hydrodynamic size, the NPs ranging from a few nanometers to an undefined level of micrometres, are separated. In the FFF technique, the NPs are resolved by a hydrodynamic pressure gradient which pushes the particles of different sizes into different channels.

To ensure high experimental throughput and keep the time between a theoretical concept and a real prototype as short as possible, we introduced stereolithography (SL) 3D printing as a simple prototyping method. The technique proposed here offers a low entry barrier for the rapid prototyping of microfluidics (LoC), enabling iterative design for laboratories without access to conventional soft-lithography carried on at cleanroom facilities. We have explored the diversity of photocurable resins to create a fully 3D printed, biocompatible and modular microfluidic platform.

Figure 1a shows an example of a first fully 3D printed LoC filtering unit. To check the performance, a mixture of 50 µL of concentrated Ag nanoparticles (5 mg/mL) of 50 nm and 200 nm diameter, diluted with 200 µL DI water, was processed through the filtering units and examined by a DLS method.
b) Experimental setup with a microfluidic filter in yellow.
c) shows the results of FFF filtering, where the larger particles, namely 200 nm diameter NPs where removed from the solution.