Furthermore, the indirect assay showed an amplification with a factor of about three as compared to the signal obtained with the direct assay

Furthermore, the indirect assay showed an amplification with a factor of about three as compared to the signal obtained with the direct assay. Open in a separate window Figure 6 Dose-response curves obtained with the Ifenprodil tartrate photonic biosensor when measuring the dilution series of plasma calibrant. in human plasma samples using the spike protein (SP), the receptor-binding domain (RBD), and the nucleocapsid protein (NP) as Ifenprodil tartrate target antigens. The results are in good agreement with several CE-IVD marked reference methods and demonstrate the potential of the aMZI biosensor technology for further development into a photonic IVD platform. Keywords: biosensor, photonics, SARS-CoV-2, antibodies, diagnostics, serology 1. Introduction Biosensors Ifenprodil tartrate are valuable tools in a wide range of application areas such as medical diagnostics, agri-food, and environmental monitoring [1,2]. Application of biosensors in point-of-care (POC) in vitro diagnostics (IVD) is promising as they may fulfill the need Elf2 for sensitive, robust, and cost-effective POC testing platforms for disease diagnosis outside of the lab. Early diagnosis and effective treatment enabled by POC diagnostics support a more efficient and Ifenprodil tartrate patient-centered healthcare system. Moreover, the availability of affordable POC diagnostics is of crucial importance for developing countries, where resources and access to healthcare facilities are limited [3]. The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic has once more emphasized the value of and the urgent need for accurate and fast POC diagnostics for outbreak control and prevention [4,5,6]. Infection with SARS-CoV-2 induces an immune response in the host that normally results in the generation of different isotype antibodies (IgM, IgG, and IgA) against specific viral antigens such as the spike protein (SP), the receptor-binding domain (RBD), and the nucleocapsid protein (NP) [7]. Seroconversion for IgG typically takes about two to three weeks after symptoms onset while IgG antibody waning typically sets in after two to three months [8,9]. Serological testing is useful for confirming if individual cases have been infected in the past, for assessing seroprevalence and overall exposure of the host population [10], and for assessing vaccination response and efficiency. Various IVD tests for SARS-CoV-2 specific antibodies are being used in the laboratory. Up till now, worldwide, 356 IVD registered serology tests are available, of which 219 are CE-IVD marked and 73 have obtained the FDA Emergency Use Authorization (EUA) [11]. Most of these tests involve enzyme-linked immunosorbent assay (ELISA), chemiluminescent immunoassay (CLIA), and lateral flow assay (LFA) test formats. Each test format has its own advantages and disadvantages: ELISA is a well-known and proven quantitative test, but the method is laborious and time-consuming and has to be performed by skilled personnel. CLIA is a highly automated and high-throughput quantitative method, but mostly depends on bulky and expensive measurement platforms. LFA is fast, simple, and relatively inexpensive, which explains why testing with lateral flow test strips has become rather customary for POC applications. However, LFA is not a quantitative test and may have a lower performance, especially with regard to sensitivity [12]. To bridge the gap between POC testing with LFA and remote (clinical lab) testing with ELISA or CLIA, several alternative POC testing formats are being developed such as lab-on-a-chip (LOC) and lab-on-a-disc (LOAD) [4,13,14,15]. Integration of microfluidics in the POC device might be beneficial as it offers possibilities for improving compactness and limiting reagent consumption and might also help in further reducing the amount of required patient sample [16]. To improve POC biomarker detection, different types of sensitive and real-time measuring biosensors have been suggested for implementation in POC devices [5,17,18,19] such as electrochemical sensors and optical sensors based on surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS), fluorescence, and chemiluminescence. Photonic biosensing technologies that have been explored for the possible use in SARS-CoV-2 serology include SPR [20,21,22,23,24], biolayer interferometry (BLI) [25], and microring resonators (MRRs) [26,27]. The last mentioned is a member of a special group of sensors called the photonic integrated Ifenprodil tartrate circuit (PIC) biosensors. PIC biosensors offer advantageous features such as a high analytical sensitivity, the capability for multiplexing and miniaturization,.