Centrifugal sedimentation immunoassays for multiplexed detection of enteric bacteria in ground water

Rapid detection of live bacteria in water using nylon filter membrane-integrated centrifugal microfluidics

Water is one of the most indispensable elements for human beings. People can live without food for a couple of weeks but cannot live without water for a couple of days. Unfortunately, drinking water is not always safe around the world; in many areas, the water for drinking could be contaminated with various microbes. However, the total viable microbe count in water still relies on culture-based methods in laboratories. Therefore, in this work, we report a novel, simple, and highly efficient strategy to detect live bacteria in water via a nylon membrane-integrated centrifugal microfluidic device. A handheld fan and a rechargeable hand warmer were utilized as the centrifugal rotor and the heat resource for reactions, respectively. The bacteria in water can be rapidly concentrated >500-fold by our centrifugation system. After incubation with water-soluble tetrazolium-8 (WST-8), the color change of the nylon membranes can be visually interpreted directly by the naked eye or recorded with a smartphone camera. The whole process can be finished in 3 h, and the detection limit can reach 10² CFU/mL. The detection range ranges from 10² CFU/mL to 10⁵ CFU/mL. The cell counting results of our platform are highly positively correlated with the results of cell counting by the conventional lysogeny broth (LB) agar plate approach or the commercial 3 M Petrifilm™ cell counting plate. Our platform provides a convenient and sensitive strategy for rapid monitoring. We highly anticipate that this platform can improve water quality monitoring in resource-poor countries in the near future.

Rapid antimicrobial susceptibility testing for low bacterial concentrations integrating a centrifuge based bacterial cell concentrator

Antibiotic resistance threatens human health worldwide. Patients infected with antibiotic-resistant bacteria require appropriate antibiotic prescriptions based on a rapid antibiotic susceptibility test (AST). Various rapid AST methods have been developed to replace the conventional AST method, which requires a long testing time. However, in most cases, these methods require a high density of bacterial samples, which leads to an additional incubation or concentration process. In this study, we introduce a rapid AST platform that allows the use of low-density bacterial samples by concentrating bacterial cells and performing AST on a single microfluidic chip. In addition, the outlet-free loading process enables the platform to load the sample and concentrate bacteria into a small field of view for single-cell detection. Using this method, rapid AST determined antibiotic resistance in three hours from a standard strain of 10³ colony-forming unit (CFU) per ml bacterial concentration. This technique can be used for the cell-based drug testing of various low-concentration bacterial samples.

Healthy humans can be a source of antibodies countering COVID-19

Here, we describe the isolation of 18 unique anti SARS-CoV-2 human single-chain antibodies from an antibody library derived from healthy donors. The selection used a combination of phage and yeast display technologies and included counter-selection strategies meant to direct the selection of the receptor-binding motif (RBM) of SARS-CoV-2 spike protein's receptor binding domain (RBD2). Selected antibodies were characterized in various formats including IgG, using flow cytometry, ELISA, high throughput SPR, and fluorescence microscopy. We report antibodies' RBD2 recognition specificity, binding affinity, and epitope diversity, as well as ability to block RBD2 binding to the human receptor angiotensin-converting enzyme 2 (ACE2) and to neutralize authentic SARS-CoV-2 virus infection in vitro. We present evidence supporting that: 1) most of our antibodies (16 out of 18) selectively recognize RBD2; 2) the best performing 8 antibodies target eight different epitopes of RBD2; 3) one of the pairs tested in sandwich assays detects RBD2 with sub-picomolar sensitivity; and 4) two antibody pairs inhibit SARS-CoV-2 infection at low nanomolar half neutralization titers. Based on these results, we conclude that our antibodies have high potential for therapeutic and diagnostic applications. Importantly, our results indicate that readily available non immune (naïve) antibody libraries obtained from healthy donors can be used to select high-quality monoclonal antibodies, bypassing the need for blood of infected patients, and offering a widely accessible and low-cost alternative to more sophisticated and expensive antibody selection approaches (e.g. single B cell analysis and natural evolution in humanized mice).

New strategies for the enumeration of enteric pathogens in water

Water quality standards for drinking water and recreational waters have long been based on the enumeration of faecal coliforms in the various water supplies, with 0 CFU Escherichia coli/100 ml for drinking water and <126 CFU generic E. coli/100 ml for recreational waters. Irrigation water will soon undergo the same scrutiny in the United States. For over 50 years the most probable number method has been used by laboratories to estimate the level of viable bacteria in a sample, but this method is labour intensive and slow, especially if large numbers of samples need to be tested. In this review, we describe some recent innovations in methods to enumerate enteric pathogens in water. These methods are based on different reasoning schemes that can be categorized as biosensors and nucleic acid-based methods. All the methods described here used natural water sources. Several were also used to survey the bacterial levels in naturally contaminated samples. The different methods vary in their limits of detection, ease of use, and potential portability. Some combine very good limits of detection with the ability to overcome technical challenges; however, there is considerable room for improvement, as none of the methods are without shortcomings.

A Fluidic Device for Immunomagnetic Separation of Foodborne Bacteria Using Self-Assembled Magnetic Nanoparticle Chains

Immunomagnetic separation has been widely used for the separation and concentration of foodborne pathogens from complex food samples, however it can only handle a small volume of samples. In this paper, we presented a novel fluidic device for the specific and efficient separation and concentration of salmonellatyphimurium using self-assembled magnetic nanoparticle chains. The laminated sawtooth-shaped iron foils were first mounted in the 3D-printed matrix and magnetized by a strong magnet to generate dot-array high gradient magnetic fields in the fluidic channel, which was simulated using COMSOL (5.3a, Burlington, MA, USA). Then, magnetic nanoparticles with a diameter of 150 nm, which were modified with the anti-salmonella polyclonal antibodies, were injected into the channel, and the magnetic nanoparticle chains were vertically formed at the dots and verified using a fluorescence inverted microscope. Finally, the bacterial sample was continuous-flow injected, and the target bacteria could be captured by the antibodies on the chains, followed by gold standard culture plating to determine the amount of the target bacteria. Under the optimal conditions, the target bacteria could be separated with a separation efficiency of 80% in 45 min. This fluidic device could be further improved using thinner sawtooth-shaped iron foils and stronger magnets to obtain a better dot-array magnetic field with larger magnetic intensity and denser dot distribution, and has the potential to be integrated with the existing biological assays for rapid and sensitive detection of foodborne bacteria.

Novel functionalities of hybrid paper-polymer centrifugal devices for assay performance enhancement

The presented work demonstrates novel functionalities of hybrid paper-polymer centrifugal devices for assay performance enhancement that leverage the advantages of both paper-based and centrifugal microfluidic platforms. The fluid flow is manipulated by balancing the capillary force of paper inserts with the centrifugal force generated by disc rotation to enhance the signal of a colorimetric lateral flow immunoassay for pathogenic E. coli. Low-cost centrifugation for pre-concentration of bacteria was demonstrated by sample sedimentation at high rotational speeds before supernatant removal by a paper insert via capillary force after deceleration. The live bacteria capture efficiency of the device was similar to a commercial centrifuge. This pre-concentrated sample when combined with gold nanoparticle immunoconjugate probes resulted in a detection limit that is 10× lower than a non-concentrated sample for a lateral flow immunoassay. Signal enhancement was also demonstrated through rotational speed variation to prevent the flow for on-device incubation and to reduce the flow rate, thus increasing the sample residence time for the improved capture of gold nanoparticle-bacteria complexes in an integrated paper microfluidic assay. Finally, multiple sequential steps including sample pre-concentration, filtration, incubation, target capture by an integrated paper microfluidic assay, silver enhancement and quenching, and index matching were completed within a single device. The detection limit was 105 colony forming units per ml, a 100× improvement over a similar paper-based lateral flow assay. The techniques utilize the advantages of paper-based microfluidic devices, while facilitating additional functionalities with a centrifugal microfluidic platform for detection performance enhancement in a low-cost, automated platform amenable to point-of-care environments.

C-reactive protein and interleukin 6 microfluidic immunoassays with on-chip pre-stored reagents and centrifugo-pneumatic liquid control

We present a fully automated centrifugal microfluidic method for particle based protein immunoassays. Stick-pack technology is employed for pre-storage and release of liquid reagents. Quantitative layout of centrifugo-pneumatic particle handling, including timed valving, switching and pumping is assisted by network simulations. The automation is exclusively controlled by the spinning frequency and does not require any additional means. New centrifugal microfluidic process chains are developed in order to sequentially supply wash buffer based on frequency dependent stick-pack opening and pneumatic pumping to perform two washing steps from one stored wash buffer; pre-store and re-suspend functionalized microparticles on a disk; and switch between the path of the waste fluid and the path of the substrate reaction product with 100% efficiency. The automated immunoassay concept is composed of on demand ligand binding, two washing steps, the substrate reaction, timed separation of the reaction products, and termination of the substrate reaction. We demonstrated separation of particles from three different liquids with particle loss below 4% and residual liquid remaining within particles below 3%. The automated immunoassay concept was demonstrated by means of detecting C-reactive protein (CRP) in the range of 1-81 ng ml^-1 and interleukin 6 (IL-6) in the range of 64-13 500 pg ml^-1. The limit of detection and quantification were 1.0 ng ml^-1 and 2.1 ng ml^-1 for CRP and 64 pg ml^-1 and 205 pg ml^-1 for IL-6, respectively.

Rapid, Portable, Multiplexed Detection of Bacterial Pathogens Directly from Clinical Sample Matrices

Enteric and diarrheal diseases are a major cause of childhood illness and death in countries with developing economies. Each year, more than half of a million children under the age of five die from these diseases. We have developed a portable, microfluidic platform capable of simultaneous, multiplexed detection of several of the bacterial pathogens that cause these diseases. This platform can perform fast, sensitive immunoassays directly from relevant, complex clinical matrices such as stool without extensive sample cleanup or preparation. Using only 1 µL of sample per assay, we demonstrate simultaneous multiplexed detection of four bacterial pathogens implicated in diarrheal and enteric diseases in less than 20 min.