Paper-Based Immunosensors with Bio-Chemiluminescence Detection.

Since the introduction of paper-based analytical devices as potential diagnostic platforms a few decades ago, huge efforts have been made in this field to develop systems suitable for meeting the requirements for the point-of-care (POC) approach. Considerable progress has been achieved in the adaptation of existing analysis methods to a paper-based format, especially considering the chemiluminescent (CL)-immunoassays-based techniques. The implementation of biospecific assays with CL detection and paper-based technology represents an ideal solution for the development of portable analytical devices for on-site applications, since the peculiarities of these features create a unique combination for fitting the POC purposes. Despite this, the scientific production is not paralleled by the diffusion of such devices into everyday life. This review aims to highlight the open issues that are responsible for this discrepancy and to find the aspects that require a focused and targeted research to make these methods really applicable in routine analysis.

Recent Advancements in Enzyme-Based Lateral Flow Immunoassays.

Paper-based lateral-flow immunoassays (LFIAs) have achieved considerable commercial success and their impact in diagnostics is continuously growing. LFIA results are often obtained by visualizing by the naked eye color changes in given areas, providing a qualitative information about the presence/absence of the target analyte in the sample. However, this platform has the potential to provide ultrasensitive quantitative analysis for several applications. Indeed, LFIA is based on well-established immunological techniques, which have known in the last year great advances due to the combination of highly sensitive tracers, innovative signal amplification strategies and last-generation instrumental detectors. All these available progresses can be applied also to the LFIA platform by adapting them to a portable and miniaturized format. This possibility opens countless strategies for definitively turning the LFIA technique into an ultrasensitive quantitative method. Among the different proposals for achieving this goal, the use of enzyme-based immunoassay is very well known and widespread for routine analysis and it can represent a valid approach for improving LFIA performances. Several examples have been recently reported in literature exploiting enzymes properties and features for obtaining significative advances in this field. In this review, we aim to provide a critical overview of the recent progresses in highly sensitive LFIA detection technologies, involving the exploitation of enzyme-based amplification strategies. The features and applications of the technologies, along with future developments and challenges, are also discussed.

Smartphone biosensor for point-of-need chemiluminescence detection of ochratoxin A in wine and coffee.

Exposure to mycotoxins, which may contaminate food and feed commodities, represents a serious health risk for consumers. Ochratoxin A (OTA) is one of the most abundant and toxic mycotoxins, thus specific regulations for fixing its maximum admissible levels in foodstuff have been established. Lateral Flow ImmunoAssay (LFIA)-based devices have been proposed as screening tools to avoid OTA contamination along the whole food chain. We report a portable, user-friendly smartphone-based biosensor for the detection and quantification of OTA in wine and instant coffee, which combines the LFIA approach with chemiluminescence (CL) detection. The device employs the smartphone camera as a light detector and uses low-cost, disposable analytical cartridges containing the LFIA strip and all the necessary reagents. The analysis can be carried out at the point of need by non-specialized operators through simple manual operations. The biosensor allows OTA quantitative detection in wine and coffee samples up to 25 µg L-1 and with limits of detection of 0.3 and 0.1 µg L-1, respectively, which are below the European law-fixed limits. These results demonstrate that the developed device can be used for routine monitoring of OTA contamination, enabling rapid and reliable identification of positive samples requiring confirmatory analysis.

A challenge in biosensors: Is it better to measure a photon or an electron for ultrasensitive detection?

Biosensor development exploiting various transduction principles is characterized by a strong competition to reach high detectability, portability and robustness. Nevertheless, a literature-based comparison is not possible, as different conditions are employed in each paper. Herein, we aim at evaluating which measurement, photons or electrons, yields better biosensor performance. Upon outlining an update in recent achievements to boost analytical performance, amperometry and chemiluminescence (CL)-based biosensors are directly compared employing the same biospecific reagents and analytical formats. Horseradish peroxidase (HRP) and hydrogen peroxide concentrations were directly measured, while glucose and mouse IgG were detected employing an enzyme paper-based biosensor and an immunosensor, respectively. Detectability was down to picomoles of hydrogen peroxide (4 pmol for CL and 210 pmol for amperometry) and zeptomoles of HRP (45 zmol for CL and 20 zmol for amperometry); IgG was detected down to 12 fM (CL) and 120 fM (amperometry), while glucose down to 17 µM (CL) and 40 µM (amperometry). Results showed that amperometric and CL biosensors offered similar detectability and analytical performance, with some peculiarities that suggest complementary application fields. As they generally provided slightly higher detectability and wider dynamic ranges, CL-based biosensors appear more suitable for point-of-care testing of clinical biomarkers, where detectability is crucial. Nevertheless, as high detectability in CL biosensors usually requires longer acquisition times, their rapidity will allocate electrochemical biosensors in real-time monitoring and wearable biosensors. The analytical challenge demonstrated that these biosensors have competitive and similar performance, and between photons and electrons the competition is still open.

Precision medicine, bioanalytics and nanomaterials: toward a new generation of personalized portable diagnostics.

The customization of disease treatment focused on genetic, environmental and lifestyle factors of individual patients, including tailored medical decisions and treatments, is identified as precision medicine. This approach involves the combination of various aspects such as the collection and processing of a large amount of data, the selection of optimized and personalized drug dosage for each patient and the development of selective and reliable analytical tools for the monitoring of clinical, genetic and environmental parameters. In this context, miniaturized, compact and ultrasensitive bioanalytical devices play a crucial role for achieving the goals of personalized medicine. In this review, the latest analytical technologies suitable for providing portable and easy-to-use diagnostic tools in clinical settings will be discussed, highlighting new opportunities arising from nanotechnologies, offering peculiar perspectives and opportunities for precision medicine.

Integrated chemiluminescence-based lab-on-chip for detection of life markers in extraterrestrial environments.

The detection of life markers is a high priority task in the exploration of the Solar System. Biochips performing in-situ multiplex immunoassays are a very promising approach alternative to gas chromatography coupled with mass spectrometry. As part of the PLEIADES project, we present the development of a chemiluminescence-based, highly integrated analytical platform for the detection of biomarkers outside of the Earth. The PLEIADES device goes beyond the current lab-on-chip approaches that still require bulky external instrumentation for their operation. It exploits an autonomous capillary force-driven microfluidic network, an array of thin-film hydrogenated amorphous silicon photosensors, and chemiluminescence bioassays to provide highly sensitive analyte detection in a very simple and compact configuration. Adenosine triphosphate was selected as the target life marker. Three bioassay formats have been developed, namely (a) a bioluminescence assay exploiting a luciferase mutant with enhanced thermal and pH stability and (b and c) binding assays exploiting antibodies or functional nucleic acids (aptamers) as biospecific recognition elements and peroxidase or DNAzymes as chemiluminescence reporters. Preliminary results, showing limits of detection in the nanomolar range, confirm the validity of the proposed approach.