Date Published: January 31, 2019
Publisher: Public Library of Science
Author(s): Kenshin Takemura, Oluwasesan Adegoke, Tetsuro Suzuki, Enoch Y. Park, Bing Xu.
Among the members of flaviviruses, the Zika virus (ZIKV) remains a potent infectious disease agent, with its associated pandemic prompting the World Health Organization (WHO) to declare it a global public health concern. Thus, rapid and accurate diagnosis of the ZIKV is needed. In this study, we report a new immunofluorescence biosensor for the detection of nonstructural protein 1 (NS1) of the ZIKV, which operates using the localized surface plasmon resonance (LSPR) signal from plasmonic gold nanoparticles (AuNPs) to amplify the fluorescence intensity signal of quantum dots (QDs) within an antigen-antibody detection process. The LSPR signal from the AuNPs was used to amplify the fluorescence intensity of the QDs. For ultrasensitive, rapid, and quantitative detection of NS1 of the ZIKV, four different thiol-capped AuNPs were investigated. Our biosensor could detect the ZIKV in a wide concentration range from 10–107 RNA copies/mL, and we found that the limit of detection (LOD) for the ZIKV followed the order Ab-L-cysteine-AuNPs (LOD = 8.2 copies/mL) > Ab-3-mercaptopropionic acid-AuNPs (LOD = 35.0 copies/mL). Immunofluorescence biosensor for NS1 exhibited excellent specificity against other negative control targets and could also detect the ZIKV in human serum.
In the mid-20th century, the causative agent, i.e., the Zika virus (ZIKV), of the vector-borne infectious disease known as Zika fever was discovered in the Zika forest of Uganda [1, 2]. It belongs to the family of genus Flavivirus and has a single, positive-stranded RNA genome. The ZIKV shares similar properties with the West Nile virus, Japanese encephalitis, yellow fever and dengue virus [3, 4]. Several outbreaks of the ZIKV have been reported since its discovery, with the most recent being in 2015 in South and North America . The outbreak in Brazil led to the discovery of a direct link between the ZIKV and congenital blindness, microcephaly, and congenital Zika syndrome known as fetal growth restriction . Most recently, a direct association between the ZIKV and Gullain-Barré neurological disorder  was reported: it can affect individuals of any age group, thus exposing many population groups to greater risk of infection. Unlike many arboviruses that can spread directly between the host and the vector, the ZIKV is known to spread via body fluids such as semen, saliva, urine and blood , thus allowing the virus to spread at an alarmingly rapid rate. Limiting the spread of the virus is problematic because many infected individuals remain asymptomatic .
A new LSPR-amplified immunofluorescence biosensor for NS1 of the ZIKV has been developed with characteristic features of rapidity, ultrasensitivity and specificity for ZIKV detection. Four Ab-conjugated thiol-capped AuNPs were investigated for their use as LSPR signal amplifiers within an antigen-antibody detection system, while the Ab-conjugated QD was used as a fluorescent signal transducer. Our results show that NS1 can be detected within a wide range of concentrations from 10 fg/mL to 1 ng/mL with an LOD of 1.28 fg/mL. Based on this result the ZIKV was detected from 10–107 RNA copies/mL with high sensitivity, rapidity and specificity using Ab-MPA-AuNPs. We have also demonstrated that Ab-MPA-AuNPs stably detected the ZIKV in a complex biological medium without any complicated processes.