The organ-on-a-chip (OoC) technology holds significant promise for biosensors and personalized medicine by enabling the creation of miniature, patient-specific models of human organs. This review studies the recent advancements in the application of polydimethylsiloxane (PDMS) microfluidics for OoC purposes. It underscores the main fabrication technologies of PDMS microfluidic systems, such as photolithography, injection molding, hot embossing, and 3D printing. The review also highlights the crucial role of integrated biosensors within OoC platforms. These electrochemical, electrical, and optical sensors, integrated within the microfluidic environment, provide valuable insights into cellular behavior and drug response. Furthermore, the review explores the exciting potential of PDMS-based OoC technology for personalized medicine. OoC devices can forecast drug effectiveness and tailor therapeutic strategies for patients by incorporating patient-derived cells and replicating individual physiological variations, helping the healing process and accelerating recovery. This personalized approach can revolutionize healthcare by offering more precise and efficient treatment options. Understanding OoC fabrication and its applications in biosensors and personalized medicine can play a pivotal role in future implementations of multifunctional OoC biosensors.

Diffuse optical spectroscopy (DOS) and diffuse optical imaging (DOI) are emerging non-invasive imaging modalities that have wide spread potential applications in many fields, particularly for structural and functional imaging in medicine. In this article, we review time-resolved diffuse optical imaging (TR-DOI) systems using solid-state detectors with a special focus on Single-Photon Avalanche Diodes (SPADs) and Silicon Photomultipliers (SiPMs). These TR-DOI systems can be categorized into two types based on the operation mode of the detector (free-running or time-gated). For the TR-DOI prototypes, the physical concepts, main components, figures-of-merit of detectors, and evaluation parameters are described. The performance of TR-DOI prototypes is evaluated according to the parameters used in common protocols to test DOI systems particularly basic instrumental performance (BIP). In addition, the potential features of SPADs and SiPMs to improve TR-DOI systems and expand their applications in the foreseeable future are discussed. Lastly, research challenges and future developments for TR-DOI are discussed for each component in the prototype separately and also for the entire system.

Solid-state Single Photon Avalanche Diodes (SPADs) have emerged as versatile photodetectors, playing a pivotal role in cutting-edge technologies such as photon counting, timing, and imaging. Their exceptional characteristics — high timing resolution, fast response, high gain, excellent quantum efficiency, and immunity to magnetic fields — make them a compelling alternative to traditional Photomultiplier Tubes (PMTs). SPADs’ unique ability to detect single photons, combined with their digital output and compact size, has positioned them as a superior choice for a wide range of applications in engineering, environmental monitoring, and healthcare. This review provides a comprehensive analysis of SPAD technology, focusing on their design principles, performance metrics, and applications. We begin by exploring the fundamental operating principles of SPADs and their key performance metrics. Next, we examine various SPAD structures across different technology nodes, offering a comparative analysis to highlight the latest advancements. Based on our review, we identify several techniques to enhance SPAD performance, including: doping profile engineering such as using high-voltage layers and doping compensation layers; upgrading optical stacks; and integration of high-speed front-end circuitry. We then introduce application-specific figures-of-merit and assess their relevance to the reviewed structures. Additionally, we address emerging trends in SPAD design, such as leveraging mask layer technology to achieve significant advancements. Finally, we conclude with an overview of research challenges, potential solutions, and future directions in SPAD technology, providing valuable insights to drive further innovations in this dynamic field.

Glass-based microfluidic devices are essential for applications such as diagnostics and drug discovery, which utilize their optical clarity and chemical stability. This review systematically analyzes pulsed laser micromachining as a transformative technique for fabricating glass-based microfluidic devices, addressing the limitations of conventional methods. By examining three pulse regimes—long (≥nanosecond), short (picosecond), and ultrashort (femtosecond)—this study evaluates how laser parameters (fluence, scanning speed, pulse duration, repetition rate, wavelength) and glass properties influence ablation efficiency and quality. A higher fluence improves the material ablation efficiency across all the regimes but poses risks of thermal damage or plasma shielding in ultrashort pulses. Optimizing the scanning speed balances the depth and the surface quality, with slower speeds enhancing the channel depth but requiring heat accumulation mitigation. Shorter pulses (femtosecond regime) achieve greater precision (feature resolution) and minimal heat-affected zones through nonlinear absorption, while long pulses enable rapid deep-channel fabrication but with increased thermal stress. Elevating the repetition rate improves the material ablation rates but reduces the surface quality. The influence of wavelength on efficiency and quality varies across the three pulse regimes. Material selection is critical to outcomes and potential applications: fused silica demonstrates a superior surface quality due to low thermal expansion, while soda–lime glass provides cost-effective prototyping. The review emphasizes the advantages of laser micromachining and the benefits of a wide range of applications. Future directions should focus on optimizing the process parameters to improve the efficiency and quality of the produced devices at a lower cost to expand their uses in biomedical, environmental, and quantum applications.

Time-resolved diffuse optical spectroscopy (TR-DOS) is an increasingly used method to determine the optical properties of diffusive media, particularly for medical applications including functional brain, breast and muscle measurements. For medical imaging applications, important features of new generation TR-DOS systems are low-cost, small size and efficient inverse modeling. To address the issues of low-cost, compact size and high integration capabilities, we have developed free-running (FR) single-photon avalanche diodes (SPADs) using 130 nm silicon complementary metal-oxide-semiconductor (CMOS) technology and used it in a TR-DOS prototype. This prototype was validated using assessments from two known protocols for evaluating TR-DOS systems for tissue optics applications. Following the basic instrumental performance protocol, our prototype had sub-nanosecond total instrument response function and low differential non-linearity of a few percent. Also, using light with optical power lower than the maximum permissible exposure for human skin, this prototype can acquire raw data in reflectance geometry for phantoms with optical properties similar to human tissues. Following the MEDPHOT protocol, the absolute values of the optical properties for several homogeneous phantoms were retrieved with good accuracy and linearity using a best-fitting model based on the Levenberg-Marquardt method. Overall, the results of this study show that our silicon CMOS-based SPAD detectors can be used to build a multichannel TR-DOS prototype. Also, real-time functional monitoring of human tissue such as muscles, breasts and newborn heads will be possible by integrating this detector with a time-to-digital converter (TDC).