Fluorescence-based detection techniques are part of an ever-expanding field and are widely used in biomedical and environmental research as a biosensing tool. These techniques have high sensitivity, selectivity, and a short response time, making them a valuable tool for developing bio-chemical assays. The endpoint of these assays is defined by changes in fluorescence signal, in terms of its intensity, lifetime, and/or shift in spectrum, which is monitored using readout devices such as microscopes, fluorometers, and cytometers. However, these devices are often bulky, expensive, and require supervision to operate, which makes them inaccessible in resource-limited settings. To address these issues, significant effort has been directed towards integrating fluorescence-based assays into miniature platforms based on papers, hydrogels, and microfluidic devices, and to couple these assays with portable readout devices like smartphones and wearable optical sensors, thereby enabling point-of-care detection of bio-chemical analytes. This review highlights some of the recently developed portable fluorescence-based assays by discussing the design of fluorescent sensor molecules, their sensing strategy, and the fabrication of point-of-care devices.

Herpes is a widespread viral infection caused by the herpes simplex virus (HSV) that has no permanent cure to date. There are two subtypes, HSV-1 and HSV-2, that are known to cause a variety of symptoms, ranging from acute to chronic. HSV is highly contagious and can be transmitted via any type of physical contact. Additionally, viral shedding can also happen from asymptomatic infections. Thus, early and accurate detection of HSV is needed to prevent the transmission of this infection. Herpes can be diagnosed in two ways, by either detecting the presence of the virus in lesions or the antibodies in the blood. Different detection techniques are available based on both laboratory and point of care (POC) devices. Laboratory techniques include different biochemical assays, microscopy, and nucleic acid amplification. In contrast, POC techniques include microfluidics-based tests that enable on-spot testing. Here, we aim to review the different diagnostic techniques, both laboratory-based and POC, their limits of detection, sensitivity, and specificity, as well as their advantages and disadvantages.

Infectious diseases caused by bacteria and viruses are highly contagious and can easily be transmitted via air, water, body fluids, etc. Throughout human civilization, there have been several pandemic outbreaks, such as the Plague, Spanish Flu, Swine-Flu, and, recently, COVID-19, amongst many others. Early diagnosis not only increases the chance of quick recovery but also helps prevent the spread of infections. Conventional diagnostic techniques can provide reliable results but have several drawbacks, including costly devices, lengthy wait time, and requirement of trained professionals to operate the devices, making them inaccessible in low-resource settings. Thus, a significant effort has been directed towards point-of-care (POC) devices that enable rapid diagnosis of bacterial and viral infections. A majority of the POC devices are based on plasmonics and/or microfluidics-based platforms integrated with mobile readers and imaging systems. These techniques have been shown to provide rapid, sensitive detection of pathogens. The advantages of POC devices include low-cost, rapid results, and portability, which enables on-site testing anywhere across the globe. Here we aim to review the recent advances in novel POC technologies in detecting bacteria and viruses that led to a breakthrough in the modern healthcare industry.

Detection of singlet oxygen using SOSG nanosensors in cancer cells produced during non-thermal plasma therapy.

All inorganic perovskite nanocrystals (CsPbX₃ NCs) have excellent optical properties with high quantum yield, size tunable absorption and emission spectra which makes them popular for a wide variety of applications. All the commonly used synthesis techniques, such as hot injection and ligand assisted reprecipitation method (LARP), use ‘good’ solvent such as dimethyl formamide, dimethyl sulfoxide or octadecene to dissolve the precursor salts. The CsPbX₃ NCs formation is triggered either by rapid injection of the dissolved precursor salt in hot mixture (hot injection) or by adding a ‘good’ solvent into a ‘poor’ solvent (LARP) that induces crystallization. Here, we present an alternative synthesis of CsPbX₃ perovskite nanocrystals in an antisolvent system, instead of a ‘good’ solvent. Crystallization in the antisolvent is induced by adding a trace amount of water, leading to the formation of highly bright CsPbX₃ nanocrystals. This method resulted in a maximum photoluminescent quantum yield of ∼91%. Furthermore, these CsPbBr₃ NCs can be modified to create core–shell structures with polymers such as silica, in the same pot. Encapsulating the NCs within a protective silica shell resulted in vastly superior water stability compared to the bare NCs. The silica coated CsPbBr₃ NCs showed strong fluorescence in water were used to label breast cancer cells, thereby demonstrating its potential as an optical contrast agent for advanced bioimaging applications. Overall, this synthesis approach requires minimal steps and time, and can be carried out in an ambient atmosphere, thereby increasing its versatility and practicality, which is particularly attractive in low-resource settings.