Pathogen Concentration Combined Solid-Phase PCR on Supercritical Angle Fluorescence Microlens Array for Multiplexed Detection of Invasive Nontyphoidal Salmonella Serovars

Phage-induced "one-to-many" FRET sensor for highly sensitive detection of Escherichia coli O157:H7

As a foodborne pathogen capable of causing severe illnesses, early detection of Escherichia coli O157:H7 (E. coli O157:H7) is crucial for ensuring food safety. While Förster resonance energy transfer (FRET) is an efficient and precise detection technique, there remains a need for amplification strategies to detect low concentrations of E. coli O157:H7. In this study, we presented a phage (M13)-induced "one to many" FRET platform for sensitively detecting E. coli O157:H7. The aptamers, which specifically recognize E. coli O157:H7 were attached to magnetic beads as capture probes for separating E. coli O157:H7 from food samples. The peptide O157S, which specifically targets E. coli O157:H7, and streptavidin binding peptide (SBP), which binds to streptavidin (SA), were displayed on the P3 and P8 proteins of M13, respectively, to construct the O157S-M13K07-SBP phage as a detection probe for signal output. Due to the precise distance (≈3.2 nm) between two neighboring N-terminus of P8 protein, the SA-labeled FRET donor and acceptor can be fixed at the Förster distance on the surface of O157S-M13K07-SBP via the binding of SA and SBP, inducing FRET. Moreover, the P8 protein, with ≈2700 copies, enabled multiple FRET (≈605) occurrences, amplifying FRET in each E. coli O157:H7 recognition event. The O157S-M13K07-SBP-based FRET sensor can detect E. coli O157:H7 at concentration as low as 6 CFU/mL and demonstrates excellent performance in terms of selectivity, detection time (≈3 h), accuracy, precision, practical application, and storage stability. In summary, we have developed a powerful tool for detecting various targets in food safety, environmental monitoring, and medical diagnosis.

Rapid detection of Salmonella typhimurium by photonic PCR-LFIS dual mode visualization

Salmonella spp., as one of the foodborne pathogens, is a severe threat to global public health. Rapid screening of salmonella spp. in contaminated food with low infective doses is the key to preventing food poisoning. In this study, a fast visualization method for detecting Salmonella typhimurium (S. typhimurium) was developed based on photonic PCR and AuNPs lateral-flow immunochromatography strip (LFIS). In addition, quantitative detection of target bacteria could be achieved by utilizing the photothermal effect of AuNPs, and the sensitivity could be improved by amplifying the photothermal signal. On the optimized conditions, the developed photonic PCR-LFIS assay was highly sensitive, with a detection limit as low as 19 cfu mL-1 of bacteria in pure culture after laser irradiation, and highly specific, exhibiting no cross-reaction with Salmonella enteritidis, Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus. Notably, S. typhimurium could be detected in pork, egg white, and milk without pre-treatment, with the recovery rates of the three samples between 81 % and 109 %. In conclusion, the photonic PCR-LFIS assay realizes sensitive, simple, and rapid detection of S. typhimurium.

Ultrasensitive and Specific Phage@DNAzyme Probe-Triggered Fluorescent Click Chemistry for On-Site Detection of Foodborne Pathogens Using a Smartphone

Rapid, specific, and on-site detection of virulent foodborne pathogenic strains plays a key role in controlling food safety. In this work, an ultrasensitive and specific Phage@DNAzyme signal probe was designed to detect foodborne pathogens. The proposed sensing probe was composed of the selected phage and functionalized DNAzyme, which realized the specific recognition of target foodborne pathogens at the strain level and the efficient catalysis of copper(II) based azide-alkyne cycloaddition (CuAAC) click reaction with fluorescent signal, respectively. As a proof of concept, the virulent Escherichia coli O157:H7 (E. coli O157:H7) as the representative analyte was first enriched and purified from the complex food samples by a 4-mercaptophenylboronic acid-modified gold slide. Following, the Phage@DNAzyme probes were specifically combined with the captured E. coli O157: H7 and catalyzed the click reaction between 3-azido-7-hydroxycoumarin and 3-butyn-1-ol with the assistance of Cu(II) to generate a visual fluorescent signal. Finally, the corresponding fluorescent signals were measured by a smartphone to quantify the target concentrations. Under optimized conditions, the bioassay exhibited a wide linear range from 10² to 10⁸ CFU/mL and the detection limit was 50 CFU/mL (S/N = 3). It was further extended to the detection of another foodborne pathogen Salmonella typhimurium with satisfying sensing performances. This work gives a new path for developing rapid, specific, and on-site detection methods for trace levels of pathogenic strains in foods.

An Overview of Organ-on-a-Chip Models for Recapitulating Human Pulmonary Vascular Diseases

Traditionally, animal models have been used for recapitulating human physiology and for studying the pathological basis of many diseases affecting humankind. Indeed, over the centuries, animal models helped advance our understanding of the biology and pathology of drug therapy for humans. However, with the advent of genomics and pharmacogenomics, we now know that conventional models cannot accurately capture the pathological conditions and biological processes in humans, although humans share many physiological and anatomical features with many animals [1-3]. Species to species variation have raised concerns about the validity and suitability of animal models for studying human conditions. Over the past decade, the development and advances in microfabrication and biomaterials have spurred the growth in micro-engineered tissue and organ models (organs-on-a-chip, OoC) as alternatives to animal and cellular models [4]. This state-of-the-art technology has been used to emulate human physiology for investigating multitudes of cellular and biomolecular processes implicated in the pathological basis of disease (Fig. 13.1) [4]. Because of their tremendous potential, OoC-based models have been listed as one of the top 10 emerging technologies in the 2016 World Economic Forum [2].

Gold Leaf-Based Microfluidic Platform for Detection of Essential Oils Using Impedance Spectroscopy

Drug delivery systems are engineered platforms for the controlled release of various therapeutic agents. This paper presents a conductive gold leaf-based microfluidic platform fabricated using xurography technique for its potential implication in controlled drug delivery operations. To demonstrate this, peppermint and eucalyptus essential oils (EOs) were selected as target fluids, which are best known for their medicinal properties in the field of dentistry. The work takes advantage of the high conductivity of the gold leaf, and thus, the response characteristics of the microfluidic chip are studied using electrochemical impedance spectroscopy (EIS) upon injecting EOs into its micro-channels. The effect of the exposure time of the chip to different concentrations (1% and 5%) of EOs was analyzed, and change in electrical resistance was measured at different time intervals of 0 h (the time of injection), 22 h, and 46 h. It was observed that our fabricated device demonstrated higher values of electrical resistance when exposed to EOs for longer times. Moreover, eucalyptus oil had stronger degradable effects on the chip, which resulted in higher electrical resistance than that of peppermint. 1% and 5% of Eucalyptus oil showed an electrical resistance of 1.79 kΩ and 1.45 kΩ at 10 kHz, while 1% and 5% of peppermint oil showed 1.26 kΩ and 1.07 kΩ of electrical resistance at 10 kHz respectively. The findings obtained in this paper are beneficial for designing suitable microfluidic devices to expand their applications for various biomedical purposes.

Multiplexed Detection of Pathogens Using Solid-Phase Loop-Mediated Isothermal Amplification on a Supercritical Angle Fluorescence Array for Point-of-Care Applications

Adaptations of new generation molecular techniques for multiplexed detection of pathogens are gaining interest in the field of point-of-care (POC) industry and onsite testing. Loop-mediated isothermal amplification (LAMP), an advanced molecular amplification technique, has proven promising due to its unique features that suits ideal for POC applications. However, application of LAMP for multiplexed detection of pathogens remains challenging because of the difficulty in the identification of specific LAMP amplicons that does not have a well-definite molecular size. In this study, we developed a solid-phase loop-mediated isothermal amplification (SP-LAMP) technique to address the challenge. Integration of LAMP with the supercritical angle fluorescence (SAF) micro-optic structures as a solid support (SS) in an array format enabled spatial separation of LAMP amplicons in a multiplexed configuration. Important parameters such as length of the SS primers, length of the primer-binding region, the effect of surface density of immobilized SS primers, and cross-reactivity among the primers of different targets were iteratively tested and optimized. With the combination of SP-LAMP and SAF techniques, it was possible to detect multiple pathogens that include Salmonella spp, Campylobater spp., Campylobacter coli, Campylobacter jejuni, avian influenza virus (AIV), and pan avian internal control (IC) under singleplex conditions. The multiplexing capacity of the SP-LAMP was demonstrated using AIV and IC with promising results. The success of SP-LAMP has opened a promising direction toward the development of a multiplex POC system for rapid detection of multiple pathogens.

A Review of Microinjection Moulding of Polymeric Micro Devices

Polymeric micro devices are gaining huge market potential in broad areas of medical devices, diagnostic devices, drug delivery, and optical applications. Current research is focusing on developing functional polymeric micro devices on a mass-production scale. Microinjection moulding is a promising technique suitable for fabricating polymeric micro devices. This review aims to summarise the primary achievements that have been achieved in various aspects of microinjection moulding of polymer micro devices, consisting of micro parts and micro surface structures. The relationships of the machine, process, rheology, tooling, micro/nanoscale replication, morphology, properties, and typical applications are reviewed in detail. Finally, a conclusion and challenges are highlighted.

A Specific and Sensitive Aptamer-Based Digital PCR Chip for Salmonella typhimurium Detection

Food poisoning and infectious diseases caused by Salmonella typhimurium (S. typhimurium) are serious public health concerns for human health and food safety. The diversity and complexity of food matrices pose great challenges for rapid and ultra-sensitive detection of S. typhimurium in food samples. A method capable of identification, detection, and quantification of S. typhimurium is essential for addressing these issues. In this study, aptamer-coated magnetic beads (Apt-MBs) are employed as capture bio-probes to specifically and selectively concentrate S. typhimurium in food samples. A self-priming chip-based digital PCR was then presented as another biosensor for on-site detection and quantification of S. typhimurium cells. The chip we developed was robust and did not require any external power for sample loading. The combination of Apt-MBs with an on-chip digital detection realized the integration into lab-on-a-chip-based biosensors for on-site monitoring of foodborne pathogens. It was possible to capture and detect S. typhimurium cells as low as 90 CFU/reaction with a capture efficiency of 94.5%. Additionally, the whole process only took about 2 h. This unique platform could also be used to monitor other target bacteria with high specificity and sensitivity by utilizing different aptamers. Furthermore, the platform has potential applications in point-of-care testing in the future.

Multiplex PCR assay based on the citE2 gene and intergenic sequence for the rapid detection of Salmonella Pullorum in chickens

Salmonella is one of the most common Gram-negative pathogens and seriously threatens chicken farms and food safety. This study aimed to establish a multiplex polymerase chain reaction (PCR) approach for the identification of different Salmonella enterica subsp. enterica. The citE2 gene and interval sequence of SPS4_00301–SPS4_00311 existed in all S. enterica subsp. enterica serovars by genomic comparison. By contrast, a 76 bp deletion in citE2 was found only in Salmonella Pullorum. Two pairs of special primers designed from citE2 and interval sequence were used to establish the multiplex PCR system. The optimized multiplex PCR system could distinguish Salmonella Pullorum and non-Salmonella Pullorum. The sensitivity of the optimized multiplex PCR system could be as low as 6.25 pg/μL and 10⁴ colony-forming units (CFU)/mL for genomic DNA and Salmonella Pullorum cells, respectively. The developed multiplex PCR assay distinguished Salmonella Pullorum from 33 different Salmonella enterica subsp. enterica serotypes and 13 non-target species. The detection of egg samples artificially contaminated with Salmonella Pullorum, Salmonella Enteritidis, and naturally contaminated 69 anal swab samples showed that results were consistent with the culture method. These features indicated that the developed multiplex PCR system had high sensitivity and specificity and could be used for the accurate detection of Salmonella Pullorum in clinical samples.

Point-of-care diagnosis of invasive non-typhoidal Salmonella enterica in bloodstream infections using immunomagnetic capture and loop-mediated isothermal amplification

Invasive non-typhoidal salmonellosis is gaining worldwide attention as an emerging disease cluster among bloodstream infections. The disease has the highest burden among immunocompromised and malnourished children in resource-limited areas due to poor access to reliable and rapid diagnostics. Point-of-care (POC) diagnostics are promising for use in such low infrastructure laboratory settings. However, there still remains a major challenge for POC testing to deal with the complexity of blood matrices in rapid detection of an extremely low concentration of blood-borne pathogens. In this work, the challenges were addressed by combining magnetic bead based pathogen concentration and Loop Mediated Isothermal Amplification (LAMP) technology. Sensitivity and performance of the combined approach were determined and compared with a direct PCR method. A direct visual detection strategy, adapted using SYTO-24 DNA intercalating dye, resulted in a limit of detection (LoD) as low as 14 CFU/mL in blood samples with a total analysis time of less than 2 h, including sample preparation. This approach has the potential for wide application as a high-throughput POC testing method to analyze pathogens in clinical, food, feed and environmental samples.

The systemic characterization of aptamer cocktail for bacterial detection studied by graphene oxide-based fluorescence resonance energy transfer aptasensor

Aptamers have gained significant attention as the molecular recognition element to replace antibodies in sensor development and target delivery. Nevertheless, it is noteworthy that unlike the wide application of polyvalent antibodies, existing researches on the combined use of heterologous aptamers with similar recognition affinity and specificity for target detection were sporadic. Herein, first, the wide existence of polyaptamer for bacteria was revealed through the summary of existing literature. Furthermore, based on the establishment of a sensitive aptamer cocktail/graphene oxide fluorescence resonance energy transfer polyaptasensor with a detection limit as low as 10 CFU/ml, the systemic characterization of aptamer cocktails in bacterial detection was carried out by taking E. coli, Vi. parahemolyticus, S. typhimurium, and C. sakazakii as the assay targets. It was turned out that the polyaptasensors for C. sakazakii and S. typhimurium owned prevalence in the broader concentration range of target bacteria. While the polyaptasensors for E. coli and V. parahemolyticus outperformed monoaptasensor mainly in the lower concentration of target bacteria. The linear relationships between fluorescence recovery and the concentration of bacteria were also discussed. The different characteristics of the bacterial cellular membrane, including the binding affinity and the robustness to variation, are analyzed to be the main reason for the diverse detection performance of aptasensors. The study here enhances a sensor detection strategy with super sensitivity. More importantly, this systemic study on the aptamer cocktail in reference to antibodies will advance the in-depth understanding and rational design of aptamer based biological recognition, detection, and targeting.

Fluorescent Semiconductor Nanorods for the Solid-Phase Polymerase Chain Reaction-Based, Multiplexed Gene Detection of Mycobacterium tuberculosis

The spread of infectious diseases with significantly high mortality rates can wreak devastating damage on global health systems and economies, underscoring the need for better disease diagnostic platforms. Solid-phase polymerase chain reaction (SP-PCR) potentially combines the advantages of conventional PCR-based diagnostics with the capability of multiplexed detection, given that the spatial separation between primers circumvents unwanted primer-primer interactions. However, the generally low efficiency of solid-phase amplification results in poor sensitivity and limits its use in detection schemes. We present an SP-PCR-based, multiplexed pulldown fluorescence assay for the detection of Mycobacterium tuberculosis (MTB), utilizing highly fluorescent oligonucleotide-functionalized CdSe/CdS and CdSe_1-xS_x/CdS nanorods (NRs) as multicolor hybridization probes. The large surface area of the NRs allows for their easy capture and pulldown, but without contributing significantly to the interparticle photon reabsorption when clustered at the pulldown sites. The NR nanoprobes were specifically designed to target the hotspot regions of the rpoB gene of MTB, which have been implicated in resistance to standard rifampicin treatment. The implementation of the semiconductor NRs as photostable multicolor fluorophores in a multiplexed SP-PCR-based detection scheme allowed for the identification of multiple hotspot regions with sub-picomolar levels of sensitivity and high specificity in artificial sputum. While this work demonstrates the utility of semiconductor NRs as highly fluorescent chromophores that can enable SP-PCR as a sensitive and accurate technique for multipathogen diagnostics, the flexible surface chemistry of the NRs should allow them to be applicable to a wide variety of detection motifs.

Dual-mode aptasensor for simultaneous detection of multiple food-borne pathogenic bacteria based on colorimetry and microfluidic chip using stir bar sorptive extraction

A dual-mode aptasensor using colorimetry and microfluidic chip (MC) together with stir bar sorptive extraction (SBSE) has been developed for firstly qualifying samples contaminated with Vibrio parahaemolyticus (V.P) and Salmonella typhimurium (S.T), then precisely determine both of them in positive samples. For this purpose, the aptamer-streptavidin encoded probes (Apt-SAEs) corresponding to different bacteria were prepared in advance. Then, a stir bar modified with 4-mercaptophenylboronic acid (MPBA) was made to extract bacteria together with Apt-SAE probes. The binding event of aptamer and target triggered the formation of two sandwich structures containing Apt-SAE, V.P or S.T. The concentration of bacteria could be enriched by 1000 times within 15 min to avoid long-time enrichment process. Finally, the stir bar was immersed in the 3,3',5,5'-Tetramethylbenzidine (TMB)-H₂O₂ solution for color development. The color could be observed by naked eyes to judge whether the analytes were present. The colorless samples were judged to be negative. For the positive samples, the adsorbed encoded probes corresponding to different bacteria would be eluted from the stir bar and rapidly analyzed by the MC. Under the optimized conditions, 100 CFU/mL of V.P or S.T or both of them could be observed by colorimetry and 35 CFU/mL of them could be detected (S/N = 3) by the MC. The assay has significant application value for on-site screening and multiple detection of food-borne pathogenic bacteria.

Temporal-Spatial-Color Multiresolved Chemiluminescence Imaging for Multiplex Immunoassays Using a Smartphone Coupled with Microfluidic Chip

Chemiluminescence (CL) bioassays have become a main technology in clinical diagnosis. However, multiplex analysis for sensitive and simultaneous determination of multiple biomarkers related to one disease in one detection run on a single chip in order to achieve fast and accurate diagnosis of diseases remains a great challenge. Herein, we report temporal-spatial-color multiresolved CL imaging strategy for multiplex label-free immunoassays using a smartphone coupled with a microfluidic chip. Temporal-spatial-color multiresolved CL imaging signals were produced by sequentially transporting coreactant H₂O₂ to the detection zones to initiate cobalt-based zeolitic imidazolate frameworks ZIF-67 catalyzed luminol-H₂O₂ CL and CL resonance energy transfer reactions. As proof-of-concept, a ZIF-67 regulated sensing strategy was developed for multiplex analysis of three model cancer biomarkers with a low detection limit of pg/mL to fg/mL, good selectivity, and low-cost, avoiding complicated labeling procedures and interferences from adjacent detection zones. This work opens a door for temporal-spatial-color multiresolved imaging for multiplex analysis.