The primary objective of medical diagnosis is to precisely detect the disease onset in a timely manner for effective treatments. The rising demand in medical diagnosis, given the rapidly aging populations, increasing population mobility and complex healthcare needs, has called for support of effective diagnostic approaches, where biosensors have provided well-suited solutions. To this end, biosensors are typically examined by the yardstick of specificity, sensitivity, dynamic range, and reliability or robustness. The advancements in biomarker discoveries and signal transduction schemes have led to biosensors of improved performances; however, challenges remain particularly for translating the biosensors into clinical uses. This chapter is therefore aimed to prepare the audience with essentials of biosensors and roadblocks associated with clinical translations. Comprehension of these prerequisites is expected to accelerate the development of biosensors from lab bench to bed.

Point-of-care technologies (POCT), defined as “the testing performed near or at the site of a patient with the result leading to a possible change in the care of the patient” by ISO 22870:2006, are transforming the healthcare system. With the growing global aging population, healthcare cost is becoming a huge burden for human society. IVD/POCT sensors can play an important role in alleviating this urgent social issue. First, they provide medical test and even therapy near the patient, saving the time and cost for commuting to hospitals. Second, with more frequent and even continuously test, more precise and even earlier diagnosis can be achieved, which further reduces the required treatment and gives doctors more information to determine more appropriate therapies. POCT sensors demand miniaturized devices and cheaper equipment. Micro/nanofabrication uses mass-production manufacturing methods to produce miniaturized sensors, which later can be packaged and fitted into a small equipment [1]. In this chapter, we will introduce the main microfabrication and nanofabrication techniques for POCT sensors.

Electrochemical biosensors combine a molecular recognition concept involving the use of biosensors to sensitively detect target analytes with an attractive electrochemistry technique to analyze a biological sample due to the direct conversion of a biological event to an electronic signal. The strength of electrochemical biosensors allows sensitive, label-free biosensing with highly temporal resolution using a miniature instrument. This chapter commences with a fundamental introduction of the electrochemical principles, as well as providing a technological comparison between general voltammetric measurements, including cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV). It continues with a broad, detailed description of various electrochemical applications ranging over ionselective electrodes, an enzyme-catalyzed / non-enzymatic glucose sensor, an aptamerbased biosensor (aptasensor), and a genosensor for nucleic acids. This chapter provides readers with a good insight into the usefulness, performance, and properties of electrochemical biosensors with many examples.

Semiconductor nanowire field-effect transistors (FETs) have attracted great interest as biosensors for point-of-care testing (POCT) because they allow label-free, real-time, ultrasensitive detection using devices that are compact, low power, and easily integrable with on-chip electronic systems. In the past twenty years, these devices have seen significant breakthroughs in various aspects of device development, such as design, fabrication, and surface functionalization, as well as in diagnostic applications, having demonstrated femtomolar detection of DNA, RNA, proteins, and small molecules. In this chapter, we highlight notable advancements in nanowire-based FET biosensors in the past decade, focusing, in particular, on biomarker detection using silicon, indium oxide and zinc oxide nanowire FET devices. Recent developments include new CMOS-compatible fabrication techniques, unconventional device configurations and detection schemes, coatings to enhance sensing stability, novel bioreceptor elements and surface modification schemes for sensitivity enhancement, as well as sample processing and portable readout systems. Furthermore, we also include studies that have used nanowire FETs in concert with pattern recognition methods for disease diagnosis using exhaled breath. The growing body of research indicates that practical solutions to long-standing issues are at hand, bringing nanowire-FET biosensors ever closer to adoption in real-world POCT applications.

This chapter provides an overview of state of the art in fluorescence detection using molecular-sized biosensors. In the past three decades, a number of activatable or tunable fluorescence biosensors have been developed, including FRET sensors, intercalating dyes, electron transfer-based sensors, fluorescein-based sensors, split GFP, biarsenical-tetracysteine sensors, aptamer sensors, H-dimer sensors, lanthanide-based sensors, carbon nanotube sensors, quencher transfer/detachment, FRET binary probes and chameleon NanoCluster Beacons. Researchers have proposed various methods to increase the dynamic range, the specificity, and the sensitivity of the aforementioned sensors. The requirements for using fluorescence sensors in biomedical imaging are reviewed, which provide general guidance for readers to conduct medical diagnosis with these newly-developed biosensing technologies. The chapter concludes with a brief perspective into the future of fluorescence-based biosensing systems.

Plasmonics has provided one of the commercially proven label-free biosensing platforms to date. Traditional surface plasmon resonance (SPR) sensors, however, suffer from moderate sensitivity because of the label-free nature. In this chapter, we review various recent approaches that have attempted to produce improved detection characteristics with unique strengths and weaknesses. We first explore plasmonic field localization for self-aligned overlap or colocalization between localized near-fields and target molecules developed for dramatically enhanced detection performance. Localized SPR sensors based on metallic nanoparticles for amplification of plasmonic optical signatures measured by target molecular interactions have also been reviewed. Phase-sensitive SPR configurations based on optical path difference as well as temporal difference control have been explored for sensitivity improvement compared with conventional intensity-based SPR sensors with measurement of angular and frequency characteristics. Relatively new analytical methods based on whispering gallery mode sensors coupled to nanostructures that support localized surface plasmon to achieve ultrahigh sensitivity that may enable single molecular detection were also described. We have also included the use of SPR imaging for high-throughput labelfree detection. Finally, surface-enhanced Raman spectroscopy using plasmonic nearfield enhancement was discussed for the amplification of molecular signals. This chapter highlights many exciting research directions that have been unraveled to develop high-performance optical label-free biosensors based on diverse plasmonic platforms.

Integrated microfluidic sensors have been developed with the understanding of fundamental laws of blood flow and its non-Newtonian properties and the advent of microfluidic technology to diagnose various diseases. Lab-on-a-chip platforms based on hemodynamics allow the highly accurate detection of the pathological changes in the behaviors of blood (i.e., red blood cells, white blood cells, and platelets) and cells. Hemorheology depends on the complex interactions of immune response and cardiovascular and other diseases. The nanofluidic systems initiated by flow characteristics remain insufficient, but the ongoing development of microfluidic and nanofluidic systems and the identification of key players and risk factors enable the study of disease onset and progression, thereby leading to a spectrum of clinically relevant findings.

Microfluidic-based (“lab-on-a-chip”) bioassays and sensors enable automated or simply-operated medical diagnostic testing in near real-time at almost any location. These diagnostic devices can be connected to networks, especially using smartphones, where the smartphone camera serves as an optical detector or means of image capture. In addition, the smartphone provides connected sensors, GPS, visual displays, user-friendly interfaces, and limited electrical power. The added communications, control, and computational capabilities foster a synergism that will widen the applications of POC devices in healthcare and facilitate data acquisition for machine learning and artificial intelligence to enhance diagnostics accuracy and expand medical knowledge. Here the technological developments for microfluidic devices in combination with consumer devices, such as smartphones, for integration into the Internet of Medical Things (IoMT), are reviewed.

In this chapter, we will review some methods and platforms related to the diagnosis of Alzheimer’s disease (AD). The global prevalence of dementia and AD shows the urgent requirement of effective treatment, where an accurate and early diagnosis plays an important role. Apart from cognitive diagnosis that clarifies the cognitive deterioration of AD, abundant clinical studies have consistently recognised the core neuropathological features and related fluid biomarkers as utile indicators for the diagnosis and prognosis of AD and its preclinical stages. In order to enhance the accuracy of detecting these biomarkers, convinced methods and platforms are essential. Here, we summarised associated platforms, including imaging platforms (e.g., positron emission tomography (PET) and structural imaging), enzyme-linked immunosorbent assays (ELISA), and matrix-assisted laser desorption/ionisation – time of flight – mass spectrometry (MALDI-TOF-MS).

Neurodegenerative diseases (NDDs) stem from the loss of neurons and related progressive disruption of psychological, cognitive, and motor functions. The development of NDDs results from either disruption or dysfunction of normal nervous tissues or the accumulation of pathologically altered proteins in the brain. Traditionally, the diagnoses are based on clinical presentations, with limited sensitivity for early diagnosis and specificity for differential diagnosis. However, advancements in the research of biomarkers and biosensing techniques have led to additional promising strategies for the molecular diagnosis of NDDs.

In this chapter, we have reviewed the clinical features, diagnostic criteria and known genetic and protein biomarkers of common NDDs. We have also discussed the importance of bioenergetics in the development of NDDs. Finally, we have placed emphasis on current developments in the detection and diagnosis of NDDs, including neuroimaging, metabolome profiling, and biosensors for NDD biomarkers. Biosensing provides a noninvasive way to diagnose NDDs at an early stage to detect alterations and abnormal products in the blood and brain tissues with high sensitivity and selectivity. This chapter is expected to provide an overview of the recent advances in diagnosing NDDs, as well as pointing out the current progress and challenges in the evaluation and treatment of NDDs and beyond.

Infectious diseases are the cause of more than 5 million deaths annually, which corresponds to approximately 10% of all deaths worldwide. Rapid and reliable diagnosis is a key aspect in reducing the number of deaths associated with infectious diseases since fast commencement of the correct treatment will not only improve patient survival but also reduce the risk of spreading the disease. Moreover, fast and reliable diagnosis prevent the wrong medicine from being prescribed, something that otherwise may lead to hmedication overuse and increased drug resistance. DNA based sensors are a group of diagnostic sensors that have attracted much attention due to their potentials for specific, sensitive, and fast detection of disease associated target molecules. In the following chapter, we will go through examples of different DNA sensors and describe the wide variety of readout systems that have been applied for DNA-sensor mediated detection of infectious diseases.

Conventional microfluidics handles liquids in a continuous fashion in microchannels. It has been widely adopted in bioanalysis for its many advantages including the ability to manipulate single cells. The footprint of the conventional microfluidic chip is small. However, it requires sophisticated external control and sensing systems to function, which limits the applications of conventional microfluidics to the laboratory environment. For point-of-care applications in the resource-limited environment, standalone diagnostic platforms, such as digital microfluidics-based platforms, are more desirable. Digital microfluidics manipulates fluids in discrete volumes in the form of droplets. In this chapter, we introduce the principle of digital microfluidics and focus on the two main forms of digital microfluidics that are actuated by the magnetic force and the electrowetting on dielectrics. We will discuss the actuation mechanisms in details and compare the pros and cons of the two most popular digital microfluidic platforms. We will also look into the applications of the digital microfluidics in biosensing and diagnostics. Example of digital microfluidicsbased nucleic acids, proteins and cells analysis will be deliberated with a focus on the suitability of those assays on digital microfluidic platforms for point-of-care applications.