In early disease stages, biomolecules of interest exist in very low concentrations, presenting a significant challenge for analytical devices and methods. Here, we provide a comprehensive overview of an innovative optical biosensing technology, termed magnetic modulation biosensing (MMB), its biomedical applications, and its ongoing development. In MMB, magnetic beads are attached to fluorescently labeled target molecules. A controlled magnetic force aggregates the magnetic beads and transports them in and out of an excitation laser beam, generating a periodic fluorescent signal that is detected and demodulated. MMB applications include rapid and highly sensitive detection of specific nucleic acid sequences, antibodies, proteins, and protein interactions. Compared with other established analytical methodologies, MMB provides improved sensitivity, shorter processing time, and simpler protocols.

In many sensitive assays, target molecules are tagged using fluorescently labeled probes and captured using magnetic beads. Here, we introduce an optical modulation biosensing (OMB) system, which aggregates the beads into a small detection area and separates the signal from the background noise by manipulating the laser beam in and out of the cluster of beads. Using the OMB system to detect human interleukin-8, we demonstrated a limit of detection of 0.02 ng/L and a 4-log dynamic range. Using Zika-positive and healthy individuals’ serum samples, we show that the OMB-based Zika IgG serological assay has 96% sensitivity and 100% specificity.

The COVID-19 pandemic highlighted the necessity of fast, sensitive, and efficient methods to test large populations for respiratory viruses. The “gold standard” molecular assays for detecting respiratory viruses, such as quantitative polymerase chain reaction (qPCR) and reverse transcription qPCR (RT-qPCR), rely on invasive swab samples and require time-consuming and labor-intensive extraction processes. Moreover, the turnaround time for RT-qPCR-based assays is too lengthy for rapid screening. Extraction-free saliva-based methods provide a non-invasive sampling process with a fast turnaround time and are suitable for high-throughput applications. However, when used with a standard RT-qPCR system, the absence of extraction significantly reduces the assays’ sensitivity. Here, using a novel optical modulation biosensing (OMB) platform, we developed a rapid and highly sensitive extraction-free saliva-based molecular assay. We blindly tested 364 paired nasopharyngeal swabs and saliva samples from suspected SARS-CoV-2 cases in Israel. Compared with the gold standard swab-based RT-qPCR assay, the sensitivity of the extraction-free saliva-based OMB assay is 90.7%, much higher than the sensitivity of extraction-free saliva-based RT-qPCR assay (77.8%) with similar specificity (95.3% and 97.6%, respectively). Moreover, out of 12 samples identified by the OMB-based assay as positive, 8 samples were collected from hospitalized patients in a COVID-19 ward and were verified to be SARS-CoV-2-positive upon admission, indicating that the actual clinical sensitivity and specificity of the OMB assay are higher. Considering its user-friendly saliva-based protocol, short and cost-effective extraction-free process, and high clinical accuracy, the OMB-based molecular assay is very suitable for high-throughput testing of large populations for respiratory viruses. IMPORTANCE: Three years after the SARS-CoV-2 outbreak, there are no molecular tests that combine low-cost and straightforward sample preparation, effective sample handling, minimal reagent and disposable requirements, high sensitivity, and high throughput required for mass screening. Existing rapid molecular techniques typically sacrifice certain requirements to meet others. Yet, localized outbreaks of novel viral diseases happen daily in different parts of the world. In this context, respiratory diseases are of specific importance, as they are frequently airborne and highly contagious, with the potential for a rapid global spread. The widely accepted opinion is that another pandemic is just a question of time. To ensure that the containment efforts for the upcoming “disease X” are successful, introducing rapid, high-throughput, and highly sensitive diagnostic methods for detecting and identifying pathogens is critical. A few months into the pandemic, saliva was suggested as a diagnostic matrix for SARS-CoV-2 detection. The collection of saliva does not require swabs and is minimally invasive. In particular, extraction-free saliva-based assays require fewer reagents and disposables, and therefore are faster and cheaper, offering an appealing alternative for low-income countries. Unfortunately, current extraction-free saliva-based detection methods, such as direct RT-qPCR or isothermal amplification, have either low sensitivity or low throughput. Therefore, we believe that the presented highly sensitive ht-OMBi platform and the extraction-free saliva-based molecular assay can become an essential tool in the infectious disease monitoring toolbox .

Rapid, sensitive, and high-throughput detection of biomarkers at low concentrations is crucial for early disease diagnosis. Many sensitive immunoassays use magnetic beads to capture fluorescently labeled targets, but quantifying these targets involves detecting the fluorescent signal from individual beads, which is time-consuming and requires a costly detection system. Additionally, there is often a trade-off between sensitivity, speed, throughput, and ease of use. A new technology, high-throughput optical modulation biosensing (OMB), enables reading a 96-well plate within 10 minutes. In OMB, a cylindrical permanent magnet immobilizes the magnetic beads at the illumination spot. Then, a laser beam is manipulated between the magnetic beads cluster and the background solution, effectively subtracting noise and reducing the need for washing and separation steps, which are usually incorporated in heterogeneous assays. This technology has evolved into a fully automated platform with high sensitivity and throughput, allowing much faster turnaround time and better sensitivity than the state-of-the-art methods, like enzyme-linked immunosorbent assay (ELISA) (for protein detection) and real-time PCR (for RNA/DNA detection). Here, we provide a comprehensive review of this technology, its development, and its applications in rapid, highly sensitive detection of proteins (e.g., human Interleukin-8) and viruses (e.g., SARS-CoV-2).