A microfluidic, dual-purpose sensor for in vitro detection of Enterobacteriaceae and biotinylated antibodies

First organic fluorescence immunoassay for the detection of Enterobacter cloacae in food matrixes

For the first time, a novel fluorescent moiety, 2-amino-4-(7-formyl-1,8-dihydropyren-2-yl)-7-hydroxy-4H-chromene-3-carbonitrile (ACC), was synthesized by an ultrasonication method. The synthesis of this moiety was confirmed via structural elucidation using FTIR and NMR spectroscopy techniques. Further, photophysical properties of the fluorescent moiety were tested using UV-visible and emission spectroscopy techniques. In this case, the moiety was tagged with an antibody of Enterobacter cloacae via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide (EDC/NHS) coupling and applied as a sensing element for the detection of Enterobacter cloacae (E. cloacae) by UV-visible and emission spectroscopy techniques. The developed fluorescent sensor detected E. cloacae via a FRET mechanism. Under optimized conditions, ACC-anti-E. cloacae detected E. cloacae in the linear range from 101 to 1010 CFU mL-1 with a limit of detection (LOD) of 10.55 CFU mL-1. The developed sensor was applied for the detection of E. cloacae in food samples such as orange, pomegranate, milk, rice, tomato, potato and onion.

Digital dipstick: miniaturized bacteria detection and digital quantification for the point-of-care

Established digital bioassay formats, digital PCR and digital ELISA, show extreme limits of detection, absolute quantification and high multiplexing capabilities. However, they often require complex instrumentation, and extensive off-chip sample preparation. In this study, we present a dipstick-format digital biosensor (digital dipstick) that detects bacteria directly from the sample liquid with a minimal number of steps: dip, culture, and count. We demonstrate the quantitative detection of Escherichia coli (E. coli) in urine in the clinically relevant range of 102-105 CFU ml-1 for urinary tract infections. Our format shows 89% sensitivity to detect E. coli in clinical urine samples (n = 28) when it is compared to plate culturing (gold standard). The significance and uniqueness of this diagnostic test format is that it allows a non-trained operator to detect urinary tract infections in the clinically relevant range in the home setting.

Microfluidic smartphone quantitation of Escherichia coli in synthetic urine

In spite of the clinical need, there is a major gap in rapid diagnostics for identification and quantitation of E. coli and other pathogens, also regarded as the biggest bottleneck in the fight against the spread of antimicrobial resistant bacterial strains. This study reports for the first time an optical, smartphone-based microfluidic fluorescence sandwich immunoassay capable of quantifying E. coli in buffer and synthetic urine in less than 25 min without sample preparation nor concentration. A limit of detection (LoD) up to 240 CFU/mL, comensurate with cut-off for UTIs (10³-10⁵ CFUs/mL) was achieved. Replicas of full response curves performed with 10⁰-10⁷ CFUs/mL of E. coli K12 in synthetic urine yielded recovery values in the range 80-120%, assay reproducibility below 30% and precision below 20%, therefore similar to high-performance automated immunoassays. The unrivalled LoD was mainly linked to the 'open fluidics' nature of the 10-bore microfluidic strips used that enabled passing a large volume of sample through the microcapillaries coated with capture antibody. The new smartphone based test has the potential of being as a rapid, point-of-care test for rule-in of E. coli infections that are responsible for around 80% of UTIs, helping to stop the over-prescription of antibiotics and the monitoring of patients with other symptomatic communicable diseases caused by E. coli at global scale.

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.

Biosensing System for Concentration Quantification of Magnetically Labeled E. coli in Water Samples

Bacterial contamination of water sources (e.g., lakes, rivers and springs) from waterborne bacteria is a crucial water safety issue and its prevention is of the utmost significance since it threatens the health and well-being of wildlife, livestock, and human populations and can lead to serious illness and even death. Rapid and multiplexed measurement of such waterborne pathogens is vital and the challenge is to instantly detect in these liquid samples different types of pathogens with high sensitivity and specificity. In this work, we propose a biosensing system in which the bacteria are labelled with streptavidin coated magnetic markers (MPs-magnetic particles) forming compounds (MLBs-magnetically labelled bacteria). Video microscopy in combination with a particle tracking software are used for their detection and quantification. When the liquid containing the MLBs is introduced into the developed, microfluidic platform, the MLBs are accelerated towards the outlet by means of a magnetic field gradient generated by integrated microconductors, which are sequentially switched ON and OFF by a microcontroller. The velocities of the MLBs and that of reference MPs, suspended in the same liquid in a parallel reference microfluidic channel, are calculated and compared in real time by a digital camera mounted on a conventional optical microscope in combination with a particle trajectory tracking software. The MLBs will be slower than the reference MPs due to the enhanced Stokes' drag force exerted on them, resulting from their greater volume and altered hydrodynamic shape. The results of the investigation showed that the parameters obtained from this method emerged as reliable predictors for E. coli concentrations.

Recent Advances in Magnetic Microfluidic Biosensors

The development of portable biosening devices for the detection of biological entities such as biomolecules, pathogens, and cells has become extremely significant over the past years. Scientific research, driven by the promise for miniaturization and integration of complex laboratory equipment on inexpensive, reliable, and accurate devices, has successfully shifted several analytical and diagnostic methods to the submillimeter scale. The miniaturization process was made possible with the birth of microfluidics, a technology that could confine, manipulate, and mix very small volumes of liquids on devices integrated on standard silicon technology chips. Such devices are then directly translating the presence of these entities into an electronic signal that can be read out with a portable instrumentation. For the aforementioned tasks, the use of magnetic markers (magnetic particles-MPs-functionalized with ligands) in combination with the application of magnetic fields is being strongly investigated by research groups worldwide. The greatest merits of using magnetic fields are that they can be applied either externally or from integrated microconductors and they can be well-tuned by adjusting the applied current on the microconductors. Moreover, the magnetic markers can be manipulated inside microfluidic channels by high gradient magnetic fields that can in turn be detected by magnetic sensors. All the above make this technology an ideal candidate for the development of such microfluidic biosensors. In this review, focus is given only to very recent advances in biosensors that use microfluidics in combination with magnetic sensors and magnetic markers/nanoparticles.

Asymmetric bead aggregation for microfluidic immunodetection

We report an asymmetric immunoaggregation assay for rapid, label-free, and sub-picomolar protein detection. Asymmetric immunoaggregated beads (AIBs) are formed when binding occurs between 1 μm magnetic (MG) and 2.8 μm polystyrene (PS) beads coated with specific antibodies for a target antigen. Detection of such aggregation is achieved by optical monitoring of AIBs in a flow under an external magnetic field. AIBs are attracted to the upper surface of the microchannel by a magnetic field and made to slide along the surface by a flow drag force. This sliding behavior is in contrast with other particles such as MG and PS beads; while attracted MG beads hardly slide due to their small size, PS beads quickly move with the flow due to the lack of magnetism. Sliding AIBs are optically monitored in a designated sensing area in the microchannel. A custom-built program code is used for counting the AIBs and further analysis of parameters such as velocity and number distributions that are correlated with target concentrations. The detection range from 54 pg mL^-1 to 54 ng mL^-1 is demonstrated for the influenza type A H1N1 nucleoprotein (NP). This immunosensing system is simple, highly sensitive, and capable of quantitative detection of antigens in a single test without fluorescent or enzyme labeling, hence is useful for the rapid detection of biomarkers in clinical and biomedical applications.