Detection of meningitis antigens in buffer and body fluids by ultrasound-enhanced particle agglutination

Ultrasonic Particle Manipulation in Glass Capillaries: A Concise Review

Ultrasonic particle manipulation (UPM), a non-contact and label-free method that uses ultrasonic waves to manipulate micro- or nano-scale particles, has recently gained significant attention in the microfluidics community. Moreover, glass is optically transparent and has dimensional stability, distinct acoustic impedance to water and a high acoustic quality factor, making it an excellent material for constructing chambers for ultrasonic resonators. Over the past several decades, glass capillaries are increasingly designed for a variety of UPMs, e.g., patterning, focusing, trapping and transporting of micron or submicron particles. Herein, we review established and emerging glass capillary-transducer devices, describing their underlying mechanisms of operation, with special emphasis on the application of glass capillaries with fluid channels of various cross-sections (i.e., rectangular, square and circular) on UPM. We believe that this review will provide a superior guidance for the design of glass capillary-based UPM devices for acoustic tweezers-based research.

On-chip immuno-agglutination assay based on a dynamic magnetic bead clump and a sheath-less flow cytometry

Immunoagglutination assay is a promising approach for the detection of waterborne analytes like virus, cells, proteins with its advantages such as a smaller amount of reagents and easier operation. This paper presents a microfluidic agglutination assay on which all the assay processes including analyte capture, agglutination, and detection are performed. The chip integrates an on-chip pump for sample loading, a dynamic magnetic bead (MB) clump for analyte capture and agglutination, and a sheath-less flow cytometry for particle detection, sizing, and counting. The chip is tested with streptavidin-coated MBs and biotinylated bovine serum albumin as a model assay, which realizes a limit of detection (LOD) of 1 pM. Then, an antigen/antibody assay using rabbit IgG and goat anti-rabbit IgG coated MBs is tested and a LOD of 5.5 pM is achieved. At last, human ferritin in 10% fetal bovine serum is tested with Ab-functionalized MBs and the detection achieves a LOD of 8.5 pM. The whole procedure takes only 10 min in total.

A rapid ultrasound particle agglutination method for HIV antibody detection: Comparison with conventional rapid HIV tests

We present the results of the feasibility and preliminary studies on analytical performance of a rapid test for detection of human immunodeficiency virus (HIV) antibodies in human serum or plasma that is an important advance in detecting HIV infection. Current methods for rapid testing of antibodies against HIV are qualitative and exhibit poor sensitivity (limit of detection). In this paper, we describe an ultrasound particle agglutination (UPA) method that leads to a significant increase of the sensitivity of conventional latex agglutination tests for HIV antibody detection in human serum or plasma. The UPA method is based on the use of: 1) a dual mode ultrasound, wherein a first single-frequency mode is used to accelerate the latex agglutination process, and then a second swept-frequency mode of sonication is used to disintegrate non-specifically bound aggregates; and 2) a numerical assessment of results of the agglutination process. The numerical assessment is carried out by optical detection and analysis of moving patterns in the resonator cell during the swept-frequency mode. The single-step UPA method is rapid and more sensitive than the three commercial rapid HIV test kits analyzed in the study: analytical sensitivity of the new UPA method was found to be 510-, 115-, and 80-fold higher than that for Capillus™, Multispot™ and Uni-Gold™ Recombigen HIV antibody rapid test kits, respectively. The newly developed UPA method opens up additional possibilities for detection of a number of clinically significant markers in point-of-care settings.

Bacterial meningitis in children under 15 years of age in Nepal

BACKGROUND

Bacterial meningitis in children is a life-threatening problem resulting in severe morbidity and mortality. For the prompt initiation of antibacterial therapy, rapid and reliable diagnostic methods are of utmost importance. Therefore, this study was designed to find out the rate of bacterial pathogens of meningitis from suspected cases by performing conventional methods and latex agglutination.

METHODS

A descriptive type of study was carried out from May 2012 to April 2013. Cerebrospinal fluid (CSF) specimens from 252 suspected cases of meningitis were subjected for Gram staining, bacterial culture and latex agglutination test. The identification of growth of bacteria was done following standard microbiological methods recommended by American Society for Microbiology. Antibiotic sensitivity testing was done by modified Kirby-Bauer disk diffusion method.

RESULTS

From the total 252 suspected cases, 7.2 % bacterial meningitis was revealed by Gram staining and culture methods whereas latex agglutination method detected 5.6 %. Gram-negative organisms contributed the majority of the cases (72.2 %) with Haemophilus influenzae as the leading pathogen for meningitis. Overall, 33.3 % mortality rate was found.

CONCLUSIONS

In conclusion, a significant rate of bacterial meningitis was found in this study prompting concern for national wide surveillance.

A low cost and high throughput magnetic bead-based immuno-agglutination assay in confined droplets

Although passive immuno-agglutination assays consist of one step and simple procedures, they are usually not adapted for high throughput analyses and they require expensive and bulky equipment for quantitation steps. Here we demonstrate a low cost, multimodal and high throughput immuno-agglutination assay that relies on a combination of magnetic beads (MBs), droplets microfluidics and magnetic tweezers. Antibody coated MBs were used as a capture support in the homogeneous phase. Following the immune interaction, water in oil droplets containing MBs and analytes were generated and transported in Teflon tubing. When passing in between magnetic tweezers, the MBs contained in the droplets were magnetically confined in order to enhance the agglutination rate and kinetics. When releasing the magnetic field, the internal recirculation flows in the droplet induce shear forces that favor MBs redispersion. In the presence of the analyte, the system preserves specific interactions and MBs stay in the aggregated state while in the case of a non-specific analyte, redispersion of particles occurs. The analyte quantitation procedure relies on the MBs redispersion rate within the droplet. The influence of different parameters such as magnetic field intensity, flow rate and MBs concentration on the agglutination performances have been investigated and optimized. Although the immuno-agglutination assay described in this work may not compete with enzyme linked immunosorbent assay (ELISA) in terms of sensitivity, it offers major advantages regarding the reagents consumption (analysis is performed in sub microliter droplet) and the platform cost that yields to very cheap analyses. Moreover the fully automated analysis procedure provides reproducible analyses with throughput well above those of existing technologies. We demonstrated the detection of biotinylated phosphatase alkaline in 100 nL sample volumes with an analysis rate of 300 assays per hour and a limit of detection of 100 pM.

Colloidal nanomaterial-based immunoassay

Nanomaterials have been widely developed for their use in nanomedicine, especially for immunoassay-based diagnosis. In this review we focus on the use of nanomaterials as a nanoplatform for colloidal immunoassays. While conventional heterogeneous immunoassays suffer from mass transfer limitations and consequently long assay time, colloidal immunosupports allow target capture in the entire volume, thus speeding up reaction kinetics and shortening assay time. Owing to their wide range of chemical and physical properties, nanomaterials are an interesting candidate for immunoassay development. The most popular colloidal nanomaterials for colloidal immunoassays will be discussed, as well as their influence on immune reactions. Recent advances in nanomaterial applications for different formats of immunoassays will be reported, such as nanomaterial-based indirect immunoassays, optical-based agglutination immunoassays, resonance energy transfer-based immunoassays and magnetic relaxation-based immunoassays. Finally, the future of using nanomaterials for homogeneous immunoassays dedicated to clinical diagnosis will be discussed.

Ultrasonic enhancement of bead-based bioaffinity assays

Ultrasonic radiation forces can be used for non-intrusive manipulation and concentration of suspended micrometer-sized particles. For bioanalytical purposes, standing-wave ultrasound has long been used for rapid immuno-agglutination of functionalized latex beads. More recently, detection methods based on laser-scanning fluorometry and single-step homogeneous bead-based assays show promise for fast, easy and sensitive biochemical analysis. If such methods are combined with ultrasonic enhancement, detection limits in the femtomolar region are feasible. In this paper, we review the development of standing-wave ultrasonic manipulation for bioanalysis, with special emphasis on miniaturization and ultrasensitive bead-based immunoassays.

A new immobilisation method to arrange particles in a gel matrix by ultrasound standing waves

Ultrasonic forces may be used to manipulate particles in suspension. For example, a standing wave ultrasound (US) field applied to a suspension moves the particles toward areas of minimal acoustic pressure, where they are orderly retained creating a predictable heterogeneous distribution. This principle of ultrasonic retention of particles or cells has been applied in numerous biotechnological applications, such as mammalian cell filtering and red blood cell sedimentation. Here, a new US-based cell immobilisation technique is described that allows manipulation and positioning of cells/particles within various nontoxic gel matrices before polymerisation. Specifically, gel immobilisation was used to directly demonstrate that the viability of yeast cells arranged by an US standing wave is maintained up to 4 days after treatment. The versatility of this immobilisation method was validated using a wide range of acoustic devices. Finally, the potential biotechnological advantages of this US-controlled particle positioning method combined with gel immobilisation/encapsulation technology are discussed.

Poly(styrene/α-tert-butoxy-ω-vinylbenzylpolyglycidol) Microspheres for Immunodiagnostics. Principle of a Novel Latex Test Based on Combined Electrophoretic Mobility and Particle Aggregation Measurements

The principle of a novel latex agglutination test based on combined results of electrophoretic mobility and particle aggregation measurements is described. Poly(styrene/alpha-tert-butoxy-omega-vinylbenzylpolyglycidol) (P(S/PGL)) microspheres were synthesized by a one step soap-free emulsion copolymerization of styrene and alpha-tert-butoxy-omega-vinylbenzylpolyglycidol macromonomer with number average molecular weight Mn = 2700 (polydispersity [Mw]/[Mn] = 1.10). Particles with monomodal size distribution (number average diameter Dn = 220 nm) and surface fraction of polyglycidol equal to f = 0.42 mol % were obtained. Human serum albumin (HSA) was covalently bound onto the surface of P(S/PGL) microspheres activated with 1,3,5-trichlorotriazine. In a model immunodiagnostic assay for anti-HSA, in which P(S/PGL) particles with covalently bound HSA have been used, the electrophoretic mobility and aggregation of microspheres were measured simultaneously. This approach allowed detection of anti-HSA in the serum in the range of anti-HSA concentrations from 0.1 to 150 microg/mL. The highest changes in electrophoretic mobility were registered for microspheres with surface concentration of immobilized HSA equal to Gamma = 9.2 x 10(-4) g/m2.

A novel ultrasound-enhanced latex agglutination test for the detection of antibodies against Mycobacterium tuberculosis in serum

A novel ultrasound-enhanced latex agglutination test is described for the detection of serum antibodies against Mycobacterium tuberculosis. The use of ultrasound to detect the low level of antibodies in serum enhances the sensitivity of the test. The technique is based on the fact that suspended latex particles become concentrated in an ultrasonic standing wave field, thereby increasing the rate of particle-particle collisions compared to the standard agglutination test procedure. Reactions were performed on piezo-ceramic wafers, which were connected to an oscillator at a frequency of 100 kHz. This method improved sensitivity significantly so that even 20 times diluted serum samples exhibited agglutination, which was clearly visible to the naked eye.

Biological effects of ultrasound: development of safety guidelines. Part II: general review

In the 1920s, the availability of piezoelectric materials and electronic devices made it possible to produce ultrasound (US) in water at high amplitudes, so that it could be detected after propagation through large distances. Laboratory experiments with this new mechanical form of radiation showed that it was capable of producing an astonishing variety of physical, chemical and biologic effects. In this review, the early findings on bioeffects are discussed, especially those from experiments done in the first few decades, as well as the concepts employed in explaining them. Some recent findings are discussed also, noting how the old and the new are related. In the first few decades, bioeffects research was motivated partly by curiosity, and partly by the wish to increase the effectiveness and ensure the safety of therapeutic US. Beginning in the 1970s, the motivation has come also from the need for safety guidelines relevant to diagnostic US. Instrumentation was developed for measuring acoustic pressure in the fields of pulsed and focused US employed, and standards were established for specifying the fields of commercial equipment. Critical levels of US quantities were determined from laboratory experiments, together with biophysical analysis, for bioeffects produced by thermal and nonthermal mechanisms. These are the basis for safety advice and guidelines recommended or being considered by national, international, professional and governmental organizations.

Rotavirus detection using ultrasound enhanced latex agglutination and turbidimetry

Application of a non-cavitating ultrasonic standing wave to suspended microparticles brings the particles into close approximation and has been used previously to enhance the performance of several diagnostic agglutination tests. The sensitivity of rotavirus detection by ultrasound enhanced latex agglutination was compared with conventional test-card agglutination. Application of ultrasound gave a 32-fold improvement in the sensitivity of detection of rotavirus antigen in buffer compared with the test card method. A novel turbidimetric approach was used to measure agglutination occurring following the test-card procedure (in place of visual examination) and following exposure of commercial rotavirus latex reagents to a 4.5 MHz ultrasonic field (in place of microscopy). The sensitivity enhancement over the conventional method achievable through ultrasonic exposure was comparable whether agglutination measurements were made visually or turbidimetrically and demonstrates the potential for turbidimetry in combination with the ultrasonic method. Turbidimetry offers an alternative to visual assessment that may be more easily incorporated into automated systems.

Ultrasound-enhanced latex immunoagglutination and PCR as complementary methods for non-culture-based confirmation of meningococcal disease

Preadmission administration of antibiotics to patients with suspected meningococcal infection has decreased the likelihood of obtaining an isolate and has stimulated development of rapid and reliable non-culture-based diagnostic methods. The sensitivity of the conventional test card latex agglutination test (TCLAT) for detection of capsular polysaccharide has been reported to be suboptimal. In the United Kingdom meningococcal DNA detection by PCR has become readily available and is now used as a first-line investigation. Recently, the performance of latex antigen detection has been markedly improved by ultrasound enhancement. Three tests for laboratory confirmation of meningococcal infection, (i) PCR assays, (ii) TCLAT, and (iii) ultrasound-enhanced latex agglutination test (USELAT), were compared in a retrospective study of 125 specimens (serum, plasma, and cerebrospinal fluid specimens) from 90 patients in whom meningococcal disease was suspected on clinical grounds. Samples were from patients with (i) culture-confirmed meningococcal disease, (ii) culture-negative but PCR-confirmed meningococcal disease, and (iii) clinically suspected but non-laboratory-confirmed meningococcal disease. USELAT was found to be nearly five times more sensitive than TCLAT. Serogroup characterization was obtained by both PCR and USELAT for 44 samples; all results were concordant and agreed with the serogroups determined for the isolates when the serogroups were available. For 12 samples negative by USELAT, the serogroup was determined by PCR; however, for 12 other specimens for which PCR had failed to indicate the serogroup, USELAT gave a result. USELAT is a rapid, low-cost method which can confirm a diagnosis, identify serogroups, and guide appropriate management of meningococcal disease contacts. A complementary non-culture-based confirmation strategy of USELAT for local use supported by a centralized PCR assay service for detection of meningococci would give the benefits of timely information and improved epidemiological data.

Ultrasonic enhancement of coated particle agglutination immunoassays: influence of particle density and compressibility

The detection rate and sensitivity (analyte concentration limit) of coated particle agglutination immunoassays are increased in ultrasonic standing waves. The influence of particle volume, density and compressibility, properties that modify the ultrasonic radiation, and interaction forces the particles experience, on assay sensitivity with latex and silica particles in the range 0.25-1.0 microm is examined here. Streptavidin-coated 0.3-microm silica particles and 0.25-microm and 1.0-microm latex particles were examined for agglutination with biotinylated bovine serum albumin (bBSA) following exposure on axis in a 4.6-MHz radial standing wave. The lowest detection limit, 2 ng/mL bBSA, was achieved with the 0.3-microm silica. The detection limit decreased with increasing latex particle size. The limit of an ultrasound-enhanced agglutination immunoassay of rabbit antimouse immunoglobulin was 6-fold better with 1.0-microm coated silica than with equal-sized latex particles. Calculations show that the particle density-dependent ultrasonic interaction force dominates the particle compressibility force for the present case. The density-dependent force on silica, but not on latex particles, is shown to be comparable in magnitude to both the long-range van der Waal's attractive force and the electrostatic repulsion between the particles. This density-dependent force may explain the improved enhancement of analyte detection by coated silica compared with latex particles.

Preliminary clinical evaluation of meningococcal disease and bacterial meningitis by ultrasonic enhancement

Antigen detection in the urine and serum may be useful in the diagnosis of suspected meningococcal disease, especially after previous antibiotic treatment. Current test card procedures using commercial agglutination kits are often too insensitive to contribute to diagnosis. Diagnosis of meningococcal disease rose from 37% with the test card procedure to 74% following ultrasonic enhancement.

Ultrasonic separations in analytical biotechnology

Cells in megahertz-frequency noncavitating ultrasonic standing waves concentrate at submillimetre distances and are, as large clumps, easily removed from suspension in flow or batch systems. An ultrasonic filter for perfusion hybridoma culture is now available. Results from small-volume prototype analytical-scale systems can inform the design of effective filter or batch-clarification systems for a wide range of cell sizes, concentrations and sample volumes. Large increases in the rates of aqueous biphasic separations and of the rates and sensitivities of analytical immunocoated particle-agglutination assays occur in standing waves. Ultrasonic manipulation is briefly compared with immunomagnetic and dielectrophoretic separations.