2. Advances in "point-of-need" testing

Nowadays, rapid tests are widely applied as an efficient screening method for conducting onsite analysis for several applications, such as food, forensic, and environmental analysis.

Still, the medical field represents the largest for a number of available systems and a variety of applications. The availability of specific and sensitive diagnostic tools that can be operated almost everywhere and by no-trained operators is strongly appreciated in low-resource settings and is regarded as a feasible way for improving access to care.

In this field, some lines of future developments can be traced.

Provided that rapid tests are intended for self-testing and also for frequent testing, the preferential specimen should be repeatedly and noninvasively collected. Moreover, noninvasive collection enables sampling children and non-collaborative patients (i.e., for testing abuse drugs, sport doping, adherence to therapy, etc.). Therefore, diagnostic devices capable of working with specimens other than blood (i.e., urine, saliva, hair, and feces) are expected to expand. Parallel to the evolution of the materials and device architecture required to achieve this task, also a robust confirmation of the clinical relevance of detecting a biomarker in an unconventional specimen is needed.

Furthermore, we are entering the era of personalized medicine that is giving new impulses to the development of diagnostic tests enabling each patient to watch over himself/herself.

Beside clinical diagnostics, rapid tests are expanding to several other fields of applications. The role played by these analytical tools in veterinary, forensic investigations, and food safety controls is worth mentioning. Application to veterinary diagnostics is the natural continuation of the human diagnostics and takes advantage especially of the development toward exploitation of unconventional biological matrices (e.g., saliva, hair) that can be collected easily from animals by the veterinarian.

The same specimens are also useful in forensic investigation as they represent samples that can be collected from non-collaborative subjects. Other aspects that are of utmost relevance for the forensic use of rapid tests are their on-site usability and speediness of response that allows for implementing actions of controls at the street level and timely intervening in dangerous situations.

Food safety controls represent a vast area of applications for rapid tests, mainly because of international regulations that are becoming more and more severe about the quality of food (i.e., the need to assess the absence of contaminants, to discover frauds, to trace production and transformation chain, to ascertain freshness, to confirm origin, etc.) and because of the globalization of trades. Key features of rapid tests that especially meet requirements in ascertain food safety are cheapness and rapidity. The first feature enables self-testing carried out by producers, transformers, and sellers, thus assuring the safety across the whole food chain. The second feature is of paramount relevance when dealing with perishable goods. It should be noticed in this context that the designing of rapid tests for food analysis implies facing a number of diverse sample typologies, each deserving an appropriate study of materials and reagents.

Synchronous to the extension of applications and thanks to the increasing scientific activity on the subject, the research on rapid tests is being drawn from the urgency of immediate marketability. Therefore, new and most efficient probes to generate the signal have been proposed, such as those based on fluorescence, chemiluminescence, and fluorescence quenching detection and on magnetic nanoparticles. Several signal enhancement strategies have been described for improving sensitivity. Besides, artificial recognition elements with increased stability and robustness compared to antibodies have been incorporated in rapid test devices. In particular, aptamerbased LFAs are the new frontiers in this area.

Finally, test design and device architecture are becoming more flexible to adapt to novel demands, such as the hyphenation with PCR amplification to detect molecular markers and the increase of multiplexing capacity.
