Microfluidic
technologies

The performance of nanophotonic devices based on resonant silicon nanoparticles (Si NPs) is critically limited by their polydispersity, introduced inherently by scalable synthesis methods such as pulsed laser ablation in liquid. To overcome this, we propose a spiral inertial microfluidic device for continuous and tunable size fractionation of laser-ablated Si NPs. The device’s separation mechanism, governed by the interplay between the inertial lift and Dean drag forces, is first optimized using mixtures of polystyrene particles and is validated through numerical simulations and analytical calculations. By applying this strategy to polydisperse Si NPs (50 nm to 1 μm), we demonstrate precise size-based sorting in a simple passive microfluidic chip by systematically varying the flow rate. High flow rates (50–60 μL/min) selectively isolate larger particles in the 745–780 nm range, whereas low flow rates (30–40 μL/min) separate smaller particles of 230–260 nm, achieving a separation resolution of R = 0.78. This work establishes a robust and scalable “lab-on-a-chip” platform that surpasses conventional batch-based techniques, enabling the production of monodisperse, high-purity Si NPs essential for advanced photonic applications, e.g., the development of high-Q metasurfaces, optical biosensors and functional elements of nanophotonic chips.

Microfluidic separation, based on sedimentation in curved channels under the action of centrifugal forces, is a powerful method for sorting nanoparticles. However, most studies demonstrate performance on model monodisperse polystyrene spheres. In this work, we implement a centrifugal microfluidic chip for a centrifuge, the parameters of which are calculated based on an existing theoretical model, to solve the practical problem of separating colloidal solutions of silicon nanoparticles (Si NPs) containing Mie-resonant Si NPs synthesized by laser ablation in liquid. We demonstrate efficient separation of the ablated colloidal solution of Si NPs (size range from 50 nm to 450 μm), leading to a significant narrowing of the nanoparticle size distribution in the outlet fractions. A key result is the successful separation of Si NPs possessing strong Mie-resonances in the visible spectrum, corresponding to diameters of approximately 120–240 nm. Thus, the presented approach demonstrates the potential of centrifugal microfluidics as an effective method for separation of polydisperse nanomaterials, in particular, Si NPs with resonant optical properties.

Quantum dots (QDs) possess unique, tunable optical properties that offer powerful opportunities for selective light-activated photochemistry and the generation of specific reactive oxygen (ROS) species. In this work, the photophysical properties and ROS generation of AgInS2 QDs were tuned by varying the Ag:In stoichiometric ratio. While all synthesized QDs maintained a uniform size (about 4 nm), increasing the Ag:In ratio induced spectral redshifts and significantly reduced photoluminescence quantum yields (PLQY). This behavior is attributed to an increased concentration of donor-acceptor defect states that facilitate nonradiative recombination. ROS generation efficiency, quantified by p-nitrosodiphenylamine (RNO) bleaching under 405 nm irradiation, was inversely correlated with PLQY. QDs with lower luminescence were 2- to 3-fold more efficient at generating ROS. This confirms that radiative recombination and ROS formation act as competing relaxation pathways of the excited state. A limitation was observed at high irradiation doses (above 200 J), where ROS-induced surface photodegradation reduced photocatalytic activity. The obtained results demonstrate that controlled stoichiometry in AgInS2 QDs allows precise tuning of their optical and photochemical behavior, enabling optimization for applications in optical sensing and photodynamic therapy.

Engineered calcium carbonate (CaCO3) particles are extensively used as drug delivery systems due to their availability, biological compatibility, biodegradability, and cost-effective production. The synthesis procedure of CaCO3 particles, however, suffers from poor reproducibility. Furthermore, reducing the size of CaCO3 particles to <100 nm requires the use of additives in the reaction, which increases the total reaction time. Here we propose on-chip synthesis and loading of nanoscaled CaCO3 particles using microfluidics. After the development and fabrication of a microfluidic device, we optimized the synthesis of CaCO3 NPs by varying different parameters such as flow rates in the microfluidic channels, concentration of reagents, and the reaction time. To prove the versatility of the used synthesis route, we performed single and double loading of CaCO3 NPs with various compounds (Doxorubicin, Cy5 or FITC conjugated with BSA, and DNA) using the same microfluidic device. Further, the on-chip loaded CaCO3 NPs were used as carriers to transfer compounds to model cells. We have developed a microfluidic synthesis method that opens up a new pathway for easy on-chip fabrication of functional nanoparticles for clinical use.

Microfluidic technology provides a solution to the challenge of continuous CaCO3 particle synthesis. In this study, we utilized a 3D-printed microfluidic chip to synthesize CaCO3 micro- and nanoparticles in vaterite form. Our primary focus was on investigating a continuous one-phase synthesis method tailored for the crystallization of these particles. By employing a combination of confocal and scanning electron microscopy, along with Raman spectroscopy, we were able to thoroughly evaluate the synthesis efficiency. This evaluation included aspects such as particle size distribution, morphology, and polymorph composition. The results unveiled the existence of two distinct synthesis regimes within the 3D-printed microfluidic chips, which featured a channel cross-section of 2 mm2. In the first regime, which was characterized by chaotic advection, particles with an average diameter of around 2 μm were produced, thereby displaying a broad size distribution. Conversely, the second regime, marked by diffusion mixing, led to the synthesis of submicron particles (approximately 800–900 nm in diameter) and even nanosized particles (70–80 nm). This research significantly contributes valuable insights to both the understanding and optimization of microfluidic synthesis processes, particularly in achieving the controlled production of submicron and nanoscale particles.