Porous silicon (PSi) biosensors offer significant potential for point-of-care diagnostics, yet their analytical performance is constrained by slow analyte diffusion into the porous matrix. To address this issue, we developed a lab-on-a-chip (LOC) device that combines a PSi immunosensor with a surface acoustic wave (SAW)-driven mixer, housed in a 3D-printed microfluidic flow cell. The platform was evaluated for the optical detection of lactoferrin (LF), a protein biomarker relevant to inflammatory bowel disease and chronic pancreatitis. Acoustic streaming generated by the SAW mixer enhanced convective mixing at the microscale and increased mass transfer of the target analyte towards the sensor surface. SAW-driven mixing achieved a 3-fold increase in the signal-to-noise ratio and a 5-fold reduction in the limit of detection compared to unmixed conditions, advancing the analytical range towards clinically significant concentrations.
The demand for a versatile and portable point-of-use (POU) sensor platform has surged due to the pandemic, especially in countries with limited medical laboratory facilities. We recently unveiled a portable, non-planar, interdigitated, flow-through, porous electrode platform that automatically measures electrochemical impedance spectroscopy (EIS) signals from various biomarkers. However, the packed powder exhibited a loss of performance over time due to displacement, leaching, and poor stability. Herein, we modified the packing strategy by synthesizing the sensing material within the channel, thereby improving adhesion, structural integrity, and stability. Leveraging the exceptional thermal stability, mechanical strength, and chemical resistance of polyimide (PI), we developed a novel fabrication approach that combines liquid-phase inversion and breath-figure techniques to create a porous PI manifold with single-walled carbon nanotubes (SWCNTs) under varying humidity conditions. Scanning electron microscope (SEM) analysis revealed that lower relative humidity (RH) conditions yield larger but less uniformly distributed pores, leading to increased channel pressure. The manifold demonstrated exceptional stability under rigorous flow conditions, withstanding a high flow rate of 30 µL/min while maintaining consistent pressure-EIS responses. The device produced a measurable proof-of-concept impedance response following exposure to a femtomolar concentration of complementary target ssDNA in 1× PBS within 15 min. A formal limit of detection was not determined in the present study. We developed a mechanically stable sensor design with improved durability under repeated flow conditions by systematically optimizing synthesis conditions and manifold configuration. This innovative fabrication strategy demonstrates the importance of packing methodology in sensor design and paves the way for robust, scalable, and efficient diagnostic solutions in resource-limited settings.
Anodized porous silicon films have been widely studied for biosensing applications, enabling label-free optical detection of numerous targets. Their appeal stems from the unique combination of tunable micro- and nanostructure with strong photonic properties, allowing precise control over pore size, layer thickness, and optical interference modes. Together with the large internal surface area, these attributes position PSi as a highly versatile optical transducer platform.
However, our work has shown that this same nanostructure also introduces a fundamental bottleneck: analyte delivery to reactive sites inside the porous matrix is strongly limited by mass transport. In PSi biosensors, target molecules must diffuse from the bulk solution to the sensor surface and then infiltrate the porous network, where transport is hindered by nanoscale confinement and coupled to surface binding kinetics. This leads to analyte depletion at pore entrances and along pore walls, effectively decoupling photonic sensitivity and surface area from molecular recognition, and imposing severe limits on detection performance at low analyte concentrations.
This talk will focus on integrated strategies to overcome these limitations by simultaneously engineering
mass transport and surface chemistry
in PSi optical biosensors for biomedical applications. We will present approaches developed by our group to enhance sensitivity using electrokinetic focusing for on-chip analyte pre-concentration, as well as microfluidic designs that promote convective transport and reduce diffusion boundary layers. In addition, we will discuss surface passivation strategies to minimize non-specific binding and the rational tailoring of capture probe conjugation to preserve accessibility and binding efficiency within the porous network. Together, these examples illustrate how aligning photonic design, mass transport, and surface chemistry enables porous silicon biosensors to move beyond diffusion-limited operation toward highly sensitive, application-relevant detection.
Surface acoustic wave (SAW) sensors, owing to their high operating frequencies, compatibility with planar micro-fabrication, and exceptional sensitivity to surface perturbations, are widely used in lab -on-a-chip and biomedical diagnostic applications. However, conventional SAW sensors operating in liquid environments suffer from substantial energy dissipation, which markedly reduces their quality factors (Q factors) and limits sensing reliability. Here, we design and fabricate a topological SAW resonant sensor for surface liquid loading by exploiting interference coupling between topological interface states and resonant cavities. The band structures are validated using a semi-analytical plane wave expansion-finite element method. The device requires only 0.04 uL of sample and enables concentration sensing of NaCl and glucose solutions, with sensitivities of up to 190 kHz/% for NaCl and 101.8 kHz% for glucose, respectively, and a concentration resolution of 0.01%. This work offers a potential technological route towards high-performance SAW biomedical chips for micro-volume sample analysis.
Bowei Wu, Ting Ma, Hanbang Deng et al.· 0 citations
This paper aims to address the critical transition of surface acoustic wave (SAW) microfluidics from microscale to nanoscale precision manipulation by deriving a systematic framework from a critical review of device performance data to analyze the inherent engineering constraints among resolution, throughput and biocompatibility, where resolution and throughput form the primary conflicting objectives, and biocompatibility serves as the power-density-defined feasibility boundary.
The review introduces a “Resolution-Throughput-Biocompatibility” triangular analysis framework. Guided by this framework, it methodically examines the working mechanisms and performance limitations of various SAW devices developed over the past fifteen years, considering two key dimensions: acoustic field modes and device configurations.
The analysis reveals that different device architectures occupy distinct positions within the triangular framework, each emphasizing specific trade-offs. The findings highlight the need for future integration of multi-physical field synergy, intelligent algorithmic control, and modular manufacturing processes to overcome bottlenecks in nanoscale manipulation, throughput and system stability.
This paper provides a novel triangular framework that systematically compares SAW device designs, offering a comprehensive perspective on the trade-offs between resolution, throughput and biocompatibility. It also outlines future directions integrating advanced control and manufacturing strategies, paving the way for practical applications in point-of-care diagnostics and online industrial monitoring.
Zhipeng Cao, Chuanjin Cui, Jingdong Bo et al.· Sensor Review· 0 citations
Cardiovascular disease remains the leading cause of mortality worldwide, placing increasing pressure on healthcare systems and highlighting the need for rapid, low-cost diagnostic solutions. Laser-driven microfabrication offers a powerful route to engineer electrochemical biosensing interfaces with tuneable morphology, conductivity, and unique surface functional groups for attaching receptors and biomolecules. Here, we report the fabrication and evaluation of two low-cost electrode platforms: planar laser-ablated gold (LAG) and gold nanostructure-modified laser-induced graphene (LIG) electrodes for biosensing C-reactive protein (CRP), an important cardiac biomarker. LIG was produced via semiconductor laser photothermal carbonization of polyimide, producing a porous sp2-rich conductive network and subsequently Au nanostructures were deposited to obtained LIG-Au electrode. Scanning electron microscopy reveals a hierarchical three-dimensional architecture for LIG-Au, in contrast to the relatively planar metallic surface of LAG. Differences in peak-to-peak separation and redox current magnitude in electrochemical measurements are attributed to variations in surface roughness, effective surface area, and underlying graphene support. Thiolated CRP-specific DNA aptamers were covalently immobilized, and the sensing performance of the LAG and LIG-Au was systematically investigated. Both aptasensors exhibited a detection limit of 50 ng ml−1 with clinically relevant linear detection ranges of 100–5000 ng ml−1 for LAG and 250–5000 ng ml−1 for LIG-Au. This work shows that the laser-printing technologies are powerful low-cost fabrication tools to produce affordable electrodes for diagnosing cardiac biomarkers.
A. Gordon, R. Blake, Damion K Corrigan et al.· Journal of Physics D: Applie...· 0 citations
To meet the stringent requirements for miniaturized and highly sensitive trace gas sensing in space-constrained scenarios, including power equipment monitoring, minimally invasive biomedical diagnostics, and in situ lithium-battery analysis, we report a MEMS-integrated fiber-tip photoacoustic spectrometer (MFPAS). The device incorporates a Fabry-Perot (F-P) photoacoustic sensor formed by directly butt-coupling a single-mode fiber (SMF) to a 3 mm x 3 mm MEMS chip with a 100-nm-thick low-pressure chemical vapor deposition (LPCVD) Si$_3$N$_4$ diaphragm. The resulting approximately 200-$\mu$m deep silicon microcavity functions simultaneously as a photoacoustic gas cell and an acoustic confinement cavity. A micro-aperture fabricated at the diaphragm periphery by focused ion beam (FIB) milling serves as both a gas diffusion channel and an acoustic high-pass filter, suppressing ambient low-frequency pressure fluctuations and stabilizing the F-P quadrature point without active servo control. In gas-phase measurements, the sensor achieves a noise-equivalent concentration (NEC) of 58.5 ppb@1s, with a rapid response time of 6 s. Benefiting from its ultra-small cavity volume of approximately 1.5 nL, the device is further adapted through structural packaging for in situ dissolved gas analysis in transformer oil, where it achieves an NEC of 230 ppb@1s and a T90 response time of 320 s in the oil phase. By combining nanoliter-scale detection volume, ppb-level sensitivity, rapid response, and wafer-scale batch fabrication compatibility, the proposed MFPAS bridges MEMS diaphragm micromachining and FIB-enabled gas exchange engineering. This design overcomes the intrinsic gas-exchange limitation of conventional sealed-diaphragm optical microphones and offers significant potential for power equipment monitoring and in situ health diagnostics.
Xingjie Liu, Mengqi Wu, Ping Lu· 0 citations
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