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Background: Melioidosis, caused by Burkholderia pseudomallei, is a severe infectious disease with high mortality rates, but is under-recognized worldwide. In endemic areas, there is a great need for simple, low-cost and rapid diagnostic tools. In a previous study we showed, that a protein multiplex array with 20 B. pseudomallei-specific antigens detects antibodies in melioidosis patients with high sensitivity and specificity. In a subsequent study the high potential of anti-B. pseudomallei antibody detection was confirmed using a rapid Hcp1 single protein-based assay. Our protein array also showed that the antibody profile varies between patients, possibly due to a combination of host factors but also antigen variations in the infecting B. pseudomallei strains. The aim of this study was to develop a rapid test, combining Hcp1 and the best performing antigens BPSL2096, BPSL2697 and BPSS0477 from our previous study, to take advantage of simultaneous antibody detection. Methods and principal findings: The 4-plex dipstick was validated with sera from 75 patients on admission plus control groups, achieving 92% sensitivity and 97–100% specificity. We then re-evaluated melioidosis sera with the 4-plex assay that were previously misclassified by the monoplex Hcp1 rapid test. 12 out of 55 (21.8%) false-negative samples were positive in our new dipstick assay. Among those, 4 sera (7.3%) were Hcp1 positive, whereas 8 (14.5%) sera remained Hcp1 negative but gave a positive reaction with our additional antigens. Conclusions: Our dipstick rapid test represents an inexpensive, standardized and simple diagnostic tool with an improved serodiagnostic performance due to multiplex detection. Each additional band on the test strip makes a false-positive result more unlikely, contributing to its reliability. Future prospective studies will seek to validate the gain in sensitivity and specificity of our multiplex rapid test approach in different melioidosis patient cohorts. Author summary: The Gram-negative environmental pathogen Burkholderia pseudomallei, causes the severe disease melioidosis. It is highly endemic in southeast Asia and northern Australia, but recent studies suggest that it is also present in many other parts of the world where it is severely underreported. The latter results from the extremely variable and non-specific clinical manifestations of the disease, lack of clinical recognition, and the global scarcity of good quality laboratories to allow diagnosis from microbiological culture. This is even more unfortunate, as early diagnosis of the disease is indispensable for an effective therapy, since B. pseudomallei is intrinsically resistant to many antibiotics used for empirical treatment in endemic areas. Therefore, the development of new, standardized and sensitive tools is of high importance for both diagnostics and epidemiology. We focused on the development of a dipstick assay, which is based on the detection of serum antibodies against four B. pseudomallei specific protein antigens. Here we present a cost effective, simple and rapid melioidosis assay with improved sensitivity that does not depend on sophisticated laboratory equipment and therefore addresses most of the before mentioned obstacles and is easy to manufacture in large scales. [ABSTRACT FROM AUTHOR]

Antibody-modified gold nanomaterials are central to many novel biosensing technologies for example the lateral flow assays technology. The combination of the specificity, provided by antibody–antigen interactions, and the unique optical properties of nanomaterials provide excellent properties for biosensors. Here, we present the use of gold nanorods (GNR) with the localized Surface Plasmon Resonance (LSPR) peak in the visible range for biomarker detection. The colour of the GNR can be tuned by the reaction conditions to provide multi-coloured gold nanorod conjugates. These antibody functionalized GNR have the potential to provide significant improvements in multiplexed analysis and sensitivity compared to conventional gold nanoparticle based lateral flow assays. However, a major challenge is the synthesis of stable conjugates that resist aggregation in samples with high ionic strength, (e.g. salt solutions) and allow highly sensitive detection of proteins. A detailed investigation of different reagents for the functionalization of gold nanorod materials are reported. An antibody modified GNR based lateral flow assay is validated for the determination of C-reactive Protein (CRP). • Gold nanorods (GNR) are described as visual labels in lateral flow assay (LFA) applications. • The sensitivity of the LFA can be optimized by varying the functionalization process of the GNR. • A highly sensitive, visually evaluable LFA was developed. [ABSTRACT FROM AUTHOR]