Open Access

Using molecularly imprinted polymers and fluorescence sensing, researchers at BAM have developed a portable solution to rapidly detect ‘forever chemicals’

Rapid, cost-effective onsite analysis is essential for food safety and diagnostics, driving the need for miniaturized, automated platforms. We present a modular bead-based microfluidic system that performs a competitive fluorescence immunoassay on superparamagnetic beads, enabling indirect detection of small organic analytes such as ochratoxin A (OTA). The platform integrates three functional modules: (i) a pearl-chain mixer for rapid competitive binding (5 min), (ii) a magnetic separation unit using an unsealed PDMS chip and removable magnet to retain beads inline, and (iii) a fluorescence detection module based on laser diode excitation and photomultiplier signal acquisition. This design allows the fluorescent competitor remaining in solution after the assay to serve as the analytical signal, simplifying cytometry-like measurements without requiring complex instrumentation. Targeting the determination of mycotoxins in flour as a use case, the system achieves ochratoxin A (OTA) quantification within 10 min using minimal sample volumes, with a limit of detection of 1.2 µg·L⁻¹ and a dynamic range spanning over four orders of magnitude. Validation with wheat flour spiked at regulatory levels demonstrates suitability for point-of-need testing in heterogeneous raw materials, such as those encountered in milling processes. Compared to ELISA and other potentially portable or onsite approaches, the device offers faster, simpler workflows while maintaining accuracy and reproducibility. Its modular architecture supports sequential sample processing without memory effects and provides a pathway for future automation, including sample preparation tailored to specific applications. This work highlights how bead-based immunoassays can be transformed into portable, user-friendly lab-on-a-chip systems, bridging laboratory and field analysis for improved food safety monitoring.

According to the World Health Organization (WHO), at least two billion people worldwide rely on drinking water sources contaminated with faeces.1 UNICEF reports that current methods for detecting faecal contamination are often expensive, time-consuming (typically requiring 18–24 hours), and generally unsuitable for on-site analysis.2 Hence, there is an urgent need for rapid analytical methods that can reliably assess drinking water quality directly in the field. Our approach utilizes the weak intrinsic fluorescence of faecal pigments such as urobilin (UB), whose emission is enhanced through complexation with Zn²⁺ in alcoholic media, known as Schlesinger’s test. However, this classical method for faecal contaminant detection has significant limitations: UB–Zn²⁺ complexes exhibit only weak fluorescence in water, their fluorescence decays over time, and is interfered by fluorescence from humic substances naturally present in surface waters. These limitations in detection in aqueous media motivated us to explore an organic–aqueous extraction system using hexanol to improve fluorescence response and signal stability. To address this, we present a dual strategy involving the use of different Zn²⁺ salts and hexanol as an extraction and fluorescence-enhancing medium. We observed a clear dependence of the fluorescence yield of UB–Zn²⁺ complexes on the counter anions of different Zn²⁺ salts. Among them, UB–Zn(NO₃)₂ complex was showing the highest fluorescence intensity in hexanol. The extraction of UB–Zn²⁺ complexes into hexanol provided enhanced and temporally stable fluorescence emission for a reliable sensing approach.3 The photophysics of the UB–Zn²⁺ complex in hexanol and Job’s plots confirmed non-trivial complex stoichiometries. Nonetheless, the developed analytical method showed sensitive (nano- and sub-nanomolar concentration) response for UB detection with negligible fluorescence interference from humic substances commonly present in environmental water. Furthermore, a 3D-printed optofluidic platform was developed to perform in-channel extraction and real-time fluorescence detection. This platform was printed all at once using a commercial SLA printer with high resolution and transparent resins. The fluidic part allowed for droplet-based extraction by chaotic advection, by means of a miniaturized pump. The optical detection combined an LED for excitation and a USB photomultiplier tube module for low fluorescence signal digital acquisition, potentially on an embedded device such as a tablet. This configuration enabled rapid, sensitive, and interference-minimized detection of faecal pigments in water, demonstrating the potential of optofluidic sensing for on-site water quality monitoring.

Perfluoroalkylic acids (PFAAs), a subclass of per- and polyfluoroalkyl substances (PFAS), are stable, widely used industrial compounds posing environmental concerns due to their persistence and toxicity. Regulatory actions and remediation strategies necessitate effective onsite analytical methods for PFAS management. We developed an optical sensing system using a fluorescent probe with a benzoxadiazole core and guanidine receptor in a droplet-based microfluidic assay to detect PFAAs in water samples with low detection limits. The PFAAs binding enhances the probe's fluorescence in organic media through protonation-mediated hydrogen bond-assisted ion pairing, exploiting two complementary supramolecular forces. Direct detection employs a liquid-liquid extraction protocol in the microfluidic device, achieving detection limits for PFOA and PFOS down to ≥0.5 µm, with a dynamic range up to 200 µm for sample volumes <100 µL. HCl/KCl buffering facilitates analyte desalting and phase transfer for quantitation from surface water. Additionally, we developed a method involving a thin polymer layer of the probe and a crosslinker on submicron silica particles for direct detection of PFAAs in water. Our approaches provide sensitive, direct recognition and indication of PFAAs, advancing the field beyond indirect sensing and offering improved background suppression, rapid assay times, and a modular design for targeting other PFAS subclasses.

The demand for compact, high-performance optical components has driven the development of increasingly sophisticated and miniaturized optical elements, often requiring complex and costly fabrication methods. In this work, we propose a cost-effective and accessible methodology for the fabrication of lenses and free-form optics using a commercially available stereolithography (SLA) 3D printer. A systematic characterization of six transparent photopolymer resins was conducted in terms of their spectroscopic, optical, and morphological properties, i.e., surface and dimensional properties. The evaluation encompassed parameters such as transmittance, autofluorescence, refractive index, and surface roughness. A straightforward and robust printing and posttreatment protocol was developed, facilitating the fabrication of optical components with over 80% transmittance, minimal intrinsic fluorescence, and a surface quality that is compatible with demanding optical applications. The fabricated components demonstrated excellent dimensional fidelity to digital designs and high reproducibility. To demonstrate the versatility of this approach, aspherical, miniaturized, and free-form lenses were designed and integrated into three fluorescence sensing systems, including oil (strip based) and chlorine (microfluidic based) detection platforms, as well as a smartphone-based SARSCoV-2 biosensor. The integration of customized 3Dprinted optics has been shown to improve signal collection and readout performance, thereby highlighting the potential of this approach for broad application by a wide range of user groups in rapid prototyping and use in miniaturized optical systems. This work represents a significant advancement in the field of additive manufacturing, particularly in relation to the development of functional photonic devices. Furthermore, it opens new prospects for sensor applications in biosensing, microfluidics, imaging, and integrated optics.