Nosocomial infections are a major concern at the worldwide level. Early and accurate identification of nosocomial pathogens is crucial to provide timely and adequate treatment. A prompt response also prevents the progression of the infection to life-threatening conditions, such as septicemia or generalized bloodstream infection. We have implemented two highly sensitive methodologies using an ultrasensitive photonic biosensor based on a bimodal waveguide interferometer (BiMW) for the fast detection of Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), two of the most prevalent bacteria associated with nosocomial infections. For that, we have developed a biofunctionalization strategy based on the use of a PEGylated silane (silane-PEG-COOH) which provides a highly resistant and bacteria-repelling surface, which is crucial to specifically detect each bacterium. Two different biosensor assays have been set under standard buffer conditions: one based on a specific direct immunoassay employing polyclonal antibodies for the detection of P. aeruginosa and another one employing aptamers for the direct detection of MRSA. The biosensor immunoassay for P. aeruginosa is fast (it only takes 12 min) and specific and has experimentally detected concentrations down to 800 cfu mL⁻¹ (cfu: colony forming unit). The second one relies on the use of an aptamer that specifically detects penicillin-binding protein 2a (PBP2a), a protein only expressed in the MRSA mutant, providing a photonic biosensor with the ability to identify the resistant pathogen MRSA and differentiate it from methicillin-susceptible S. aureus (MSSA). Direct, label-free, and selective detection of whole MRSA bacteria has been achieved, making possible the direct detection of also 800 cfu mL⁻¹. According to the signal-to-noise (S/N) ratio of the device, a theoretical limit of detection (LOD) of around 49 and 29 cfu mL⁻¹ was estimated for P. aeruginosa and MRSA, respectively. Both results obtained under standard conditions reveal the great potential this interferometric biosensor device has as a versatile and specific tool for bacterial detection and quantification, providing a rapid method for the identification of nosocomial pathogens within the clinical requirements of sensitivity for the diagnosis of infections.

Portable point-of care (POC) devices for in vitro diagnostics will be a milestone for the achievement of universal healthcare and environmental protection. The main goal is to reach a rapid, user-friendly and highly sensitive portable tool which can provide immediate results in any place at any time while having a competitive cost. Integrated optical (IO) waveguide based-biosensors are the most suitable candidates to achieve this ambitious objective. They are able to operate in real samples (such as blood, urine, wastewater…) affording relevant sensitivities even under a label-free scheme. In addition, arrays of IO sensors for multiplexed analysis can be integrated in lab-on-chip (LOC) platforms, providing a truly cost-effective fabrication and miniaturization. Among the different IO biosensors, interferometric ones have demonstrated the highest sensitivity for label-free detection ever reported. Although the first interferometric biosensors were developed in the early nineties, they focused mainly on preliminary proof-of-concept studies; only recently the resilient potential of interferometric biosensors as highly advanced POC devices has firmly emerged. This review provides an overview of the state-of-the art in photonic interferometric biosensors, their main biofunctionalisation routes and their integration in LOC platforms, while maintaining a special focus on the real analytical applications achieved so far.

Spontaneous bacterial peritonitis is an acute bacterial infection of ascitic fluid; it has a high incidence in cirrhotic patients and it is associated with high mortality. In such a situation, early diagnosis and treatment is crucial for the survival of the patient. However, bacterial analysis in ascitic fluid is currently based on culture methods, which are time-consuming and laborious. We report here the application of a photonic interferometer biosensor based on a bimodal waveguide (BiMW) for the rapid and label-free detection of bacteria directly in ascitic fluid. The device consists of a straight waveguide in which two modes of the same polarization interfere while interacting with the external medium through their evanescent fields. A bimolecular event occurring on the sensor area of the device (e.g. capturing bacteria) will differently affect each light mode, inducing a variation in the phase of the light exiting at the output of the waveguide. In this work, we demonstrate the quantitative detection of Bacillus cereus in buffer medium and Escherichia coli in undiluted ascitic fluid from cirrhotic patients. In the case of Bacillus cereus detection, the device was able to specifically detect bacteria at relevant concentrations in 12.5min and in the case of Escherichia coli detection, the analysis time was 25min. Extrapolation of the data demonstrated that the detection limits of the biosensor could reach few bacteria per milliliter. Based on the results obtained, we consider that the BiMW biosensor is positioned as a promising new clinical tool for user-friendly, cost-effective and real-time microbiological analysis.

In this review, we present the current trends in photonic biosensors, focusing on devices based on lab-on-a-chip (LOC) systems capable of simultaneously detecting multiple real-life diseases on a single platform. The first section lists the advantages and challenges of building LOC platforms based on integrated optics. Some of the most popular materials for the fabrication of microfluidic cells are also shown. Then, a review of the latest developments in biosensors using the evanescent wave detection principle is provided; this includes interferometric biosensors, ring resonators, and photonic crystals, including a brief description of commercial solutions, if available. Then, a review of the latest advances in surface plasmon resonance (SPR) biosensors is presented, including localized-SPRs (LSPRs). A brief comparison between the benefits and required improvements on each kind of biosensor is discussed at the end of each section. Finally, prospects in the field of LOC biosensors based on integrated optics are glimpsed.

A label‐free interferometric transducer showing a theoretical detection limit for homogeneous sensing of 5 × 10^–8 RIU, being equivalent to a protein mass coverage resolution of 2.8 fg mm^–2, is used to develop a high sensitive biosensor for protein detection. The extreme sensitivity of this transducer combined with a selective bioreceptor layer enables the direct evaluation of the human growth hormone (hGH) in undiluted urine matrix in the 10 pg mL^–1 range. magnified image

Aquaculture is an expanding economic sector that nourishes the world’s growing population due to its nutritional significance over the years as a source of high-quality proteins. However, it has faced severe challenges due to significant cases of environmental pollution, pathogen outbreaks, and the lack of traceability that guarantees the quality assurance of its products. Such context has prompted many researchers to work on the development of novel, affordable, and reliable technologies, many based on nanophotonic sensing methodologies. These emerging technologies, such as surface plasmon resonance (SPR), localised SPR (LSPR), and fibre-optic SPR (FO-SPR) systems, overcome many of the drawbacks of conventional analytical tools in terms of portability, reagent and solvent use, and the simplicity of sample pre-treatments, which would benefit a more sustainable and profitable aquaculture. To highlight the current progress made in these technologies that would allow them to be transferred for implementation in the field, along with the lag with respect to the most cutting-edge plasmonic sensing, this review provides a variety of information on recent advances in these emerging methodologies that can be used to comprehensively monitor the various operations involving the different commercial stages of farmed aquaculture. For example, to detect environmental hazards, track fish health through biochemical indicators, and monitor disease and biosecurity of fish meat products. Furthermore, it highlights the critical issues associated with these technologies, how to integrate them into farming facilities, and the challenges and prospects of developing plasmonic-based sensors for aquaculture.