An immunochromatographic test for serological diagnosis of scrub typhus

A fluorescent immunochromatographic test (FM-ICT) was developed for rapid detection of anti-Orientia tsutsugamushi antibodies in serum samples. The FM-ICT was constructed based on the dual-antigen sandwich method. Truncated 56 kDa outer membrane protein of O. tsutsugamushi strain SJ, was expressed in E. coli and mixed with those of Ptan and Gillam strains. A thin line of the protein mixture was precisely sprayed across a nitrocellulose membrane making this the "Test" line. Polyclonal antibodies (pAbs) to O.tsutsugamushi were sprayed in another line across the membrane making this the "Control" line. Fluorescent microspheres conjugated 56 kDa proteins reacting with sample serum will be captured on the "Test" line if the sample contains antibodies to O.tsutsugamushi. Several experimental parameters were optimized. After optimizing the reaction procedure, the results are visible, within 6 min, with the naked eye under ultraviolet light. The limit of detection (LOD) was determined to be 7.63 ng/mL with prepared polyclonal antibodies. No cross-reaction was observed with sera samples from other febrile diseases. In clinical evaluations, the strips showed 94.92% sensitivity (106/112) and 93.75% specificity (56/60). The FM-ICT we developed will provide a new tool for on-site diagnosis of scrub typhus.

A novel photothermal sensing probe based on violet phosphorus for sensitive immunochromatographic sensing detection

Photothermal immunochromatographic sensor is an emerging detection technology, and it is important to develop new sensing probes with excellent photothermal performance to improve its detection performance. In the present study, a novel photothermal sensing probe based on violet phosphorus nanosheets with satisfactory photothermal conversion efficiency (31.1 %) was reported for the first time. A photothermal immunochromatographic sensor using the above probe was applied for visual and photothermal detection of diethylstilbestrol. The diethylstilbestrol concentration was inversely proportional to photothermal sensing signal and showed a good linear correlation in the range of 0.75 ∼ 50 μg·L-1. After optimizing, the visual and photothermal detection limits were 6 μg·L-1 and 0.56 μg·L-1, respectively. The recovery rates in tap water, milk and pork samples ranged from 82.2 % to 115.2 %, with a coefficient of variation (CV) ranging from 2.0 % to 10.8 %. This work not only structured a new type of photothermal probe, but also expanded the application range of violet phosphorus.

Development of a sensitive immunochromatographic method using lanthanide fluorescent microsphere for rapid test for PPRV antibody

Peste des petits ruminants virus (PPRV) causes a very devastating disease in sheep and goats. Rapid diagnosis and immunisation have been identified as key strategies for successful prevention of the disease. Therefore, a sensitive fluorescent microsphere immunochromatography test strips (FM-ICTS) was developed for rapid detection of special antibodies of PPRV in goats and sheep serum. The FM-ICTS were successfully prepared by fluorescent microspheres (FM) as tracer, which were covalently coupled to PPRV nucleocapsid protein (NP). The NP and monoclonal antibody of NP were separately dispensed onto a nitrocellulose membrane as test and quality control lines, respectively. The critical threshold for determining negative or positive through the ratio of the fluorescent signal of the test line and the control line (T/C) is 0.050. The repeatability of the FM-ICTS was excellent, with an overall average CV of 3.17 %. The detection limit of this assay was 1:5120. Additionally, the FM-ICTS no cross reaction with the sera of other related diseases was observed, only reacting with anti-PPRV serum. 70 serum samples were tested by FM-ICTS and commercial ELISA kit, and the results showed good agreement. Overall, a promising pen-side diagnostic tool was developed for the rapid qualitatively/semi-quantitatively detection of PPRV antibodies within 15 min.

Measurement of trace bisphenol A in drinking water with combination of immunochromatographic detection technology and SERS method

Sensitive and selective detection of target analyte is very important in many fields such as commodity inspection and quality monitoring. In this work, based on the principle of competitive immunoassay, surface-enhanced Raman spectroscopy (SERS) was used to establish a rapid and highly sensitive method for the detection of trace amounts of bisphenol A in water. Here, Raman molecule 5,5-dithiobis-2-nitrobenzoic acid and anti-BPA antibody were conjugated with Au (core)@Ag (shell) nanoparticle to serve as SERS nanoprobe. After the SERS nanoprobe is combined with the substance to be tested, it uses the siphon effect to pass through the test line and the charging line on the test strip. And the Raman test was performed on the T line with a Raman spectrometer. The detection limitation was 0.1 pg/mL. Compared with the reported gas chromatography, liquid chromatography, fluorescence analysis, and other detection methods, SERS ICA does not demand complicated sample preparation procedures, and has the advantages of simple detection methods, quick results, High sensitivity, good specificity, and low technical demands for laboratory environment and testers. In addition, Raman spectrometers have gradually developed to be portable, making it easier to meet the needs of on-site rapid and highly sensitive detection, and will show broad prospects for applications in the fields of biomedical diagnosis and food safety monitoring.

Evaluation of three immunochromatographic tests in COVID-19 serologic diagnosis and their clinical usefulness

Results of three rapid immunochromatographic tests (ICTs) were compared with those obtained with two automated immunoassays for evaluation of their usefulness. One hundred fifty-nine patients and 67 healthy volunteers were included. Different assays demonstrate 41–45% of diagnostic sensitivities and 91–98% of specificities, with substantial agreement (89.3–91.2%), but a high percentage of weak positive results (13–22%) was observed with ICTs. ICTs performances were comparable to those of automated immunoassays. ICTs could have a role as screening approach due to their easy usability. Subjective interpretation, significant rate of uncertain results, uncertainty on viral antigens source are undoubtedly drawbacks.

Development of a film-based immunochromatographic microfluidic device for malaria diagnosis

In this study, a novel film-based immunochromatographic microfluidic device (IMD) has been developed for malaria diagnosis. A microfluidic channel was patterned on a polyethylene terephthalate (PET) double-sided adhesive film using a plotting cutter and was assembled with a polycarbonate (PC) film. The PC film used for the probe immobilization layer was activated using oxygen plasma treatment to modify the film surface with avidin-biotin linker to immobilize a capture antibody. A fluorescent labeled Pan type mAb conjugate was prepared for signal indicator after undergoing a sandwich enzyme-linked immunosorbent assay (ELISA). Target antigens include Plasmodium falciparum (P. falciparum) lactate dehydrogenase (LDH) and Plasmodium vivax (P. vivax) LDH which were injected into the sample inlet. Target antigens combined with the conjugate and then flowed to the detection chamber where two test dots and a control dot (Ctrl) exist. In the presence of P. falciparum LDH, three detection dots including test dot 1 (T1), test dot 2 (T2) and Ctrl revealed fluorescence signals where P. falciparum mAb, Pan type pLDH mAb and goat anti-mouse IgG were immobilized, respectively. When P. vivax LDH was present, T2 and Ctrl dots showed fluorescence signals while no signal was detected with the negative control. P. falciparum LDH and P. vivax LDH were successfully detected on the IMD with a detection limit of 50 ng/mL and 100 ng/mL, respectively. The IMD provides a point-of-care diagnosis platform which is able to analyze pathogenic bacteria and viruses that can be applied in the field of clinical diagnosis and food safety testing.

Diagnosis of rotavirus infection in a vaccinated population: Is a less sensitive immunochromatographic method more suitable for detecting wild-type rotavirus than real-time RT-PCR?

BACKGROUND

Diagnosis of wild-type rotavirus disease may be complicated by the detection of vaccine-derived virus which can be detected in stool samples following immunisation. We evaluate an immunochromatographic assay and real-time RT-PCR to determine which is more suitable for the detection of wild-type rotavirus.

OBJECTIVES

To compare the Ct values of wild-type rotavirus and Rotarix determined by real-time RT-PCR. To establish the Ct value corresponding to the limit of detection of the immunochromatographic Combi-Strip method (Coris, BioConcept).

STUDY DESIGN

Retrospective review of real-time RT-PCR Ct values was performed on 100 samples tested by a pan-rotavirus assay (n = 50 wild-type, n = 50 Rotarix). Secondly the limit of detection of the Combi-Strip assay was determined by testing; wild-type rotavirus (n = 33, Ct range 6.85-34.26) samples, Rotarix (n = 9, Ct range 20.86-34.26) samples and rotavirus negative (n = 21) samples.

RESULTS

The median Ct of 50 wild-type rotavirus was Ct 12.43; range 6.11-32.66 compared with the median of 50 Rotarix, Ct 29.09; range 18.91-35.28, p=<0.0001. The limit of detection of the Combi-Strip method was approximately Ct 18. The 21 rotavirus negative samples were negative by real-time RT-PCR and Combi-Strip.

CONCLUSIONS

We found the Ct value was significantly lower, and therefore the viral load higher, for wild-type rotavirus compared to detectable Rotarix. The Combi-Strip assay detects most wild-type infections; however, it lacks sensitivity to detect low-level wild-type rotavirus and, beneficially, is unlikely to detect Rotarix. It is not a more suitable method than real-time RT-PCR when a definitive rotavirus result is required.

Development of quantitative immunochromatographic assay for rapid and sensitive detection of carbohydrate antigen 19-9 (CA 19-9) in human plasma

A quantitative immunochromatographic assay (QIA) was developed by using gold nanoparticle (GNP)-based lateral flow strip biosensor (LFSB) and a portable strip reader for rapid and sensitive quantitation of Carbohydrate Antigen 19-9 (CA 19-9) in human plasma. CA 19-9 is a biomarker that has been associated with cancers (such as pancreatic and colorectal cancers) and various non-cancerous diseases. The principle is based on sandwich-type immunoreactions between gold nanoparticle (GNP)-labelled detection antibody, anti-CA 19-9 capture antibody and CA 19-9to capture the GNPs on the test zone of LFSB. The accumulation of GNPs on the test zone gave a red line whose intensity was read with a portable strip reader to quantify the concentration of CA 19-9. Assay parameters including the membrane type, antibody concentration, amount of GNP-anti-CA 19-9 conjugates and the components of the running buffer were optimized to obtain the best sensitivity and reproducibility of the assay. The detection limit of the assay was determined to be 5UmL^-1 (S/N=3) with a linear range of 5UmL^-1-100UmL^-1. CA 19-9 concentrations in healthy human and pancreatic cancer patient plasma samples were successfully evaluated using the developed quantitative immunochromatographic assay (QIA), and the results were in accordance with that obtained with enzyme linked immunosorbent assay (ELISA). The developed assay shows great promise for clinical application and biomedical diagnosis, particularly in limited resource settings.