Flow Analysis

Flow analysis encompasses a suite of automated methods for introducing, mixing and detecting analytes within a continuous or segmented stream. Traditionally established platforms—flow injection analysis (FIA), sequential injection analysis (SIA) and lab-in-syringe—have evolved through manifold commutation, on-line preconcentration and hyphenation with optical or electrochemical detectors. The advent of microfluidics has miniaturised these concepts into channel networks only tens of micrometres wide, enabling rapid mixing, reduced reagent consumption and point-of-care applicability. Within these microsystems, innovations in plasmonic nanostructures, magnetic trapping agents and stimuli-responsive materials have driven the integration of surface-enhanced Raman spectroscopy (SERS), fluorescence and chemiluminescence for ultrasensitive detection. Recent progress spans magnetic nanochain stir bars for parallel bioassays, under-oil open microfluidic reactors for multiphase reactions, and printed microdevices embedding multifunctional colloids. Collectively, these advances underscore global trends towards portable, high-throughput and green analytical workflows for environmental monitoring, clinical diagnostics and chemical synthesis.

Research from Nature Portfolio

Researchers have introduced a magnetic-nanochain-integrated biochip that unites on-chip mixing, target separation and SERS signal transduction within a planar microfluidic layout. Self-assembled Fe₃O₄/Au nanochains serve as nanoscale stirrers and affinity agents, driving rapid enrichment of protein biomarkers and microbial targets in microlitre samples. This valve-free design achieves ultrafast, parallel analysis of cancer proteins and bacteria in under ten minutes, illustrating how functionalised magnetic elements can accelerate assay kinetics in clinical settings.

A visualization-enhanced under-oil open microfluidic system has been developed for in situ Raman characterisation of multi-phase reactions. A semi-transparent silicon nanolayer positioned under the oil interface suppresses background Raman noise while preserving gas permeability and clog-free operation. This platform has demonstrated real-time monitoring of gas-evolving reactions and gas-liquid interactions, highlighting its potential for label-free molecular sensing in chemical and biochemical studies.

A plasmonic microfluidic sensor for sensitive in situ detection of organic molecules employs chemically synthesised Ag nanoparticles immobilised in a continuous microchannel. Finite-difference time-domain simulations guided optimisation of nanoparticle size and distribution to generate uniform electromagnetic hotspots. Reproducible SERS spectra of methylene blue at nanomolar levels have been obtained with high signal uniformity, emphasising the role of controlled nanoparticle fabrication in environmental monitoring.

Research from all publishers

A femtosecond-laser nanoparticle-implantation technique has produced homogeneous Au nanoparticle arrays on flexible polymer films, which are integrated into microfluidic chips for SERS analysis. The laser-implanted strips deliver electromagnetic enhancements exceeding 10⁸, enabling picogram-per-litre detection of malachite green. Robust embedment affords multiple cleaning cycles without sensitivity loss, and real-time monitoring of on-chip oxidation reactions has elucidated reaction pathways.

A comprehensive review of microfluidic SERS systems for disease diagnostics surveys continuous-flow, microarray-embedded, droplet and gradient platforms. It highlights strategies for multiplexed biomarker panels, automated workflows and clinical translation, while identifying challenges in substrate standardisation and fluidic integration. The survey maps future directions for point-of-care diagnostic devices employing SERS microfluidics.

Advances in 3D-printed microfluidic devices incorporate Janus magnetic-plasmonic Fe₃O₄/Au nanostars as colloidal SERS substrates. External magnetic fields localise the nanostars at detection zones, boosting Raman signals for environmental and biomedical analytes. Rapid prototyping and magnetic trapping enable quantitative assays in under thirty minutes with minimal sample volumes, pointing to scalable, low-cost sensing solutions.

Flow Analysis publication trend

The graph below shows the total number of articles in flow analysis across all publications each year (not limited to Nature Index journals).

Technical terms

Flow Injection Analysis (FIA): A technique in which discrete sample plugs are injected into a continuous carrier stream and mixed en route to a detector, enabling high-throughput assays.

Microfluidics: The manipulation and control of small fluid volumes (microlitres to picolitres) within networks of channels tens to hundreds of micrometres in diameter, affording precise mixing and rapid analysis.

Surface-Enhanced Raman Spectroscopy (SERS): A vibrational spectroscopy method that exploits plasmonic nanostructures to amplify otherwise weak Raman signals by several orders of magnitude.

Plasmonic Nanostructures: Nanometre-scale metallic features (often Au or Ag) that support collective electron oscillations, creating intense local electromagnetic fields.

Hotspots: Localised regions near plasmonic nanostructures where electromagnetic fields are dramatically intensified, leading to enhanced Raman scattering.

References

1. Flow Analysis: Looking Back and Forward. Journal of the Brazilian Chemical Society (2018).
2. Magnetic nanochain integrated microfluidic biochips. Nature Communications (2018).
3. Visualization-enhanced under-oil open microfluidic system for in situ characterization of multi-phase chemical reactions. Nature Communications (2024).
4. Organic Molecule Detection Based on SERS in Microfluidics. Scientific Reports (2019).
5. Femtosecond laser-induced nanoparticle implantation into flexible substrate for sensitive and reusable microfluidics SERS detection. International Journal of Extreme Manufacturing (2024).
6. Microfluidics for disease diagnostics based on surface-enhanced raman scattering detection. Nano Convergence (2024).
7. 3D Printed Microfluidic Device for Magnetic Trapping and SERS Quantitative Evaluation of Environmental and Biomedical Analytes. ACS Applied Materials & Interfaces (2021).