SARS-CoV-2 spike protein detection using slightly tapered no-core fiber-based optical transducer

Efficient one-step immobilization of DNA probes on 1DZnO nanoplatforms targeting a low-mutation region of SARS-CoV-2

Fabricating cost-effective biosensors with rapid response times is highly desirable during pandemic scenarios, where accuracy, swift detection, and portability are crucial for making prompt decisions. The design and conceptualization of these devices at early stages are critical for enhancing their output responses. In this work, we implemented a one-step immobilization strategy for DNA probes targeting a low-mutation region from the envelope protein of SARS-CoV-2 onto one-dimensional ZnO nanostructures (1DZnO) to achieve high detection efficiency. First, DNA probes were designed to select a highly conserved region (L28-A36) among SARS-CoV-2 subvariants using bioinformatic analysis. Then, dynamic simulations were performed to estimate the binding affinity of DNA to 1DZnO, where phosphate molecules were identified as the functional groups with the highest affinity to the ZnO surface, followed by the sugar rings and the base pairs. In addition, linear interaction energies and their average contributions were calculated for the ssDNA/ZnO interfaces. Computational simulations were correlated to experimental techniques, where suitable DNA immobilization and target detection were confirmed by FTIR, photoluminescence (PL), transmission electron microscopy, and elemental mapping, corroborating the adsorption of DNA across the entire 1DZnO surface. Intense peaks related to C-C, C=C, C=N, P-O, and N-H were identified as the most important by FTIR characterizations, whereas PL showed a distinctive shift in deep level emission band between 520-530 nm, with a partial quenching of the near band emission signal, obtaining as well variations in the calculated bandgap. In summary, it is suggested that structural oxygen vacancies of 1DZnO nanoplatforms provide a significant proportion of active available sites for an easy and strong interaction with the phosphate backbone of DNA, enhancing physical adsorption. Furthermore, molecular validation by PCR confirmed the long-term stability of immobilized DNA probes, probing their suitability for further biosensing devices.

Rapid assays of SARS-CoV-2 virus and noble biosensors by nanomaterials

The COVID-19 outbreak caused by SARS-CoV-2 in late 2019 has spread rapidly across the world to form a global epidemic of respiratory infectious diseases. Increased investigations on diagnostic tools are currently implemented to assist rapid identification of the virus because mass and rapid diagnosis might be the best way to prevent the outbreak of the virus. This critical review discusses the detection principles, fabrication techniques, and applications on the rapid detection of SARS-CoV-2 with three categories: rapid nuclear acid augmentation test, rapid immunoassay test and biosensors. Special efforts were put on enhancement of nanomaterials on biosensors for rapid, sensitive, and low-cost diagnostics of SARS-CoV-2 virus. Future developments are suggested regarding potential candidates in hospitals, clinics and laboratories for control and prevention of large-scale epidemic.

Temperature-insensitive label-free SARS-CoV-2 spike protein detection based on complementary refractive index and temperature dependence of multi-mode interference and grating resonance

We demonstrated temperature-insensitive, label-free detection of SARS-CoV-2 spike protein (SSP) by harnessing the complementary refractive index and temperature dependence of multi-mode interference (MMI) created by a no-core fiber (NCF) and phase-matched resonance generated by a long-period fiber grating (LPFG). To combine MMI and grating resonance, primarily sensitive to the surrounding medium refractive index (SMRI) and ambient temperature, respectively, a fiber-optic transducer was fabricated by splicing an NCF segment with an LPFG inscribed on double-clad fiber. The transducer was functionalized with human ACE2 receptors to selectively capture SSP. The functionalized sensor head exhibited high SSP selectivity, with overall average wavelength displacements of ∼253.33 and ∼160.00 pm in PBS and saliva, respectively, for SSP with concentrations ranging from 1 to 104 ng/mL. These spectral shifts are associated with localized SMRI modulations on the sensor surface induced by specific binding between SSP and ACE2. We also examined the cross-reactivity of the sensor head for MERS-CoV spike protein to confirm its SSP specificity. Moreover, we proved the capability of temperature-independent SSP detection and ambient temperature measurement by scrutinizing the temperature effect on the sensor performance. Our functionalized fiber transducer showed great promise as a temperature-insensitive and portable platform for rapid SSP detection.