Performance evaluation of free-space fibre optic detection in a lab-on-chip for microorganism

This paper describes the development of a lab-on-chip (LOC) device that can perform reliable online detection in continuous-flow systems for microorganisms. The objective of this work was to examine the performance of a fibre optic detection system integrated into a LOC device. The microfluidic system was fabricated using dry film resist (DFR), integrated with multimode fibre pigtails in the LOC. Subsequently, the performance of the fibre optic detection was evaluated by its absorbance spectra, detection limit, repeatability and reproducibility, and response time. The analysis was carried out using a constant flow rate for three different types of microorganisms which are Escherichia coli, Saccharomyces cerevisiae, and Aeromonas hydrophila. Under the experimental conditions used in this study, the detection limit of 1 0 × 105 cells/mL for both A. hydrophila and E. coli, while a detection limit of 1 0 × 106 cells/mL for S. cerevisiae cells were measured. The results also revealed that the device showed good repeatability with standard deviations less than 0.2 for A. hydrophila and E. coli, while standard deviations for S. cerevisiae were larger than 1.0. The response times for A. hydrophila, E. coli, and S. cerevisiae were 104 s, 122 s, and 78 s, respectively, although significant errors were recorded for all three species for reproducibility experiment. It was found that the device showed generally good sensitivity, with the highest sensitivity towards S. cerevisiae. These findings suggest that an integrated LOC device, with embedded multimode fibre pigtails, can be a reliable instrument for microorganism detection

Development and applications of nanobiosensors for sustainable agricultural and food industries : Recent developments, challenges and perspectives

The increasing global population and limited natural resources are amongst major challenges in the sustainability of agricultural and food industries, together with the rapid shrinking of land and increasing production cost. Based on the application of nanobiosensors, natural resources can be utilised more efficiently. Particularly, nanobiosensors can be used in a wide range of applications throughout the agri-food route, ranging from detection of soil condition, crop diseases caused by pest/pathogen, management of severe infections, and diagnostic tools for detection of pests during storage and ensures final quality assurance. Here, we review the various recent applications of nanobiosensors in agricultural and food industries. The advantages and limitations are also discussed to provide useful insights to both academic and industrial researchers. Moreover, recent patents have been discussed to provide the latest trends in biosensors for agri-food industry to maintain sustainable development

Developing Biosensor Technology to Monitor Biofilm Formation on Voice Prosthesis in Throat Cancer Patients Following Total Laryngectomy

Voice prostheses (used to replace an excised larynx in laryngectomy patients) are often colonised by the yeast Candida albicans, yet no monitoring technology for C. albicans biofilm growth until these devices fail. With the current interest in smart technology, understanding the electrical properties of C. albicans biofilm formation is necessary. There has been great interest in Passive Radio Frequency Identification (RFID) for use with implantable devices as they provide a cost-effective approach for sensing. The main drawback of RFID sensors is the need to overcome capacitive loading of human tissue and, thus, low efficiency to produce a high read range sensor design. This is further complicated by the size restriction on any RFID design to be implemented within a voice prosthesis as this medical device is limited to less than 3 cm in overall size. In order to develop such a voice prosthesis sensor, we looked at three separate aspects of C. albicans colonisation on medical devices within human tissue. To understand if it is possible to detect changes within a moist environment (such as the mouth), we developed a sensor capable of detecting minute dielectric changes (accuracy of ± 0.83 relative permittivity and ± 0.05 S·m-1 conductivity) within a closed system. Once we understood that detection of dielectric changes within a liquid solution were possible, to overcome human tissue capacitive loading of RFID sensors. Adjusting backing thickness or adding a capacitive shunt into the design could limit this tissue effect and even negate the variability seen between human tissues. Without developing these methods, implementation of any RFID device would be difficult as human tissue variability would not be compensated for properly. Finally, biofilm growth in terms electrical properties. As C. albicans biofilm matures, there is a loss in capacitance (the biofilm becomes increasingly hydrophobic) prior to 24 hours after which the biofilm thickness shifts the resonance leading to a slow gain in capacitance. Understanding all of these aspects allowed us to develop two final voice prosthesis sensors producing read ranges above 60 cm and 10 cm within a tissue phantom. Ultimately, this showed the possibility of developing cost-effective passive RFID sensor technology for monitoring microbial biofilm formation within human tissue, leading to more effective real-time clinical care

Point-of-Need DNA Testing for Detection of Foodborne Pathogenic Bacteria

Foodborne pathogenic bacteria present a crucial food safety issue. Conventional diagnostic methods are time-consuming and can be only performed on previously produced food. The advancing field of point-of-need diagnostic devices integrating molecular methods, biosensors, microfluidics, and nanomaterials offers new avenues for swift, low-cost detection of pathogens with high sensitivity and specificity. These analyses and screening of food items can be performed during all phases of production. This review presents major developments achieved in recent years in point-of-need diagnostics in land-based sector and sheds light on current challenges in achieving wider acceptance of portable devices in the food industry. Particular emphasis is placed on methods for testing nucleic acids, protocols for portable nucleic acid extraction and amplification, as well as on the means for low-cost detection and read-out signal amplification

Silicon-Based Optical Sensors for Fungal Pathogen Diagnostics

The last years have witnessed a link between the COVID-19 pandemic with increasing numbers of vulnerable patients and globally emerging incidences of severe drug-resistant fungal infections, thus, calling for rapid, reliable, and sensitive diagnostic tools for fungal infections. However, despite strong warnings from health authorities, such as the World Health Organization, concerning the fatal consequences of the global spread of drug-resistant pathogenic fungi, progress in fungal infection diagnosis and therapy is still limited. Today, gold standard methods for revealing resistance and susceptibility in pathogenic fungi, namely antifungal susceptibility testing (AFST), require several days for completion, and thus this lengthy process can adversely affect antifungal therapy and further promote the spread of resistance. In this work, the use of photonic silicon chips consisting of micropatterned diffraction gratings as sensitive sensors for rapid AFST of clinically relevant fungal pathogens is investigated. These photonic chips provide a surface for the colonization of microbial pathogens at a liquid-solid interface and serve as the optical transducer element for label-free monitoring of fungal growth by detecting real-time changes in the white light reflectance. These sensor elements are used to track morphological changes of fungi in the presence of clinically relevant antifungals at varying concentrations to rapidly determine the minimum inhibitory concentration (MIC) values that help to classify pathogens as resistant or susceptible. We show that by careful design of the chip dimensions, this optical method can extend from bacteria, through yeasts, to filamentous fungi for accelerated AFST, which is at least three times faster than current gold standard methods and can provide same-day results. Moreover, a 3D-printed microfluidic gradient generator was designed to complement the assay and provide an integrated system, which can potentially be employed in point-of-care settings. This gradient generator produces the two-fold dilution series of clinically relevant antimicrobials in an automated manner and is interfaced with the photonic silicon chips to include a complete, on-chip, label-free, and phenotypic assay. Using the bacterial species Escherichia coli and ciprofloxacin as a model pathogen-drug combination, MIC values can be expeditiously determined within 90 minutes compared to current clinical practices, which typically require up to 24 h for bacterial species

Three dimensional optofluidic devices for manipulation of particles and cells

Optical forces offer a powerful tool for manipulating single cells noninvasively. Integration of optical functions within microfluidic devices provides a new freedom for manipulating and studying biological samples at the micro scale. In the pursuit to realise such microfluidic devices with integrated optical components, Ultrafast Laser Inscription (ULI) fabrication technology shows great potential. The uniqueness and versatility of the technique in rapid prototyping of 3D complex microfluidic and optical elements as well as the ability to perform one step integration of these elements provides exciting opportunities in fabricating novel devices for biophotonics applications. The work described in this thesis details the development of three dimensional optofluidic devices that can be used for biophotonics applications, in particular for performing cell manipulation and particle separation. Firstly, the potential of optical forces to manipulate cells and particles in ULI microfluidic channels is investigated. The ability to controllably displace particles within a ULI microchannel using a waveguide positioned orthogonal to it is explored in detail. We then prototype a more complex 3D device with multiple functionalities in which a 3D optofluidic device containing a complex microchannel network and waveguides was used for further investigations into optical manipulation and particle separation. The microfluidic channel network and the waveguides within the device possess the capability to manipulate the injected sample fluid through hydrodynamic focusing and optically manipulate the individual particles, respectively. This geometry provided a more efficient way of investigating optical manipulation within the device. Finally, work towards developing a fully optimised 3D cell separator device is presented. Initial functional validation was performed by investigating the capability of the device to route particles through different outlet channels using optical forces. A proof of concept study demonstrates the potential of the device to use for cell separation based on the size of the cells. It was shown that both passive and active cell separation is possible using this device