Exploring near-field sensing efficiency of complementary plasmonic metasurfaces for immunodetection of tumor markers

A review on hybridization of plasmonic and photonic crystal biosensors for effective cancer cell diagnosis

Cancer causes one in six deaths worldwide, and 1.6 million cancer patients face annual out-of-pocket medical expenditures. In response to these, portable, label-free, highly sensitive, specific, and responsive optical biosensors are under development. Therefore, in this review, the recent advances, advantages, performance analysis, and current challenges associated with the fabrication of plasmonic biosensors, photonic crystals, and the hybridization of both for cancer diagnosis are assessed. The primary focus is on the development of biosensors that combine different shapes, sizes, and optical properties of metallic and dielectric nanoparticles with various coupling techniques. The latter part discusses the challenges and prospects of developing effective biosensors for early cancer diagnosis using dielectric and metallic nanoparticles. These data will help the audience advance research and development of next-generation plasmonic biosensors for effective cancer diagnosis.

Plasmonic metasurface enhanced by nanobumps for label-free biosensing of lung tumor markers in serum

Plasmonic metasurface biosensing has excellent potential in label-free detection of tumor biomarkers. In general, a variety of plasmonic metasurface nanofabrication leads to various degree of metallic surface roughness. However, the metasurface roughness effects on plasmonic sensing of tumor markers have been barely reported. Here we fabricate high-roughness (HR) gold nanohole metasurfaces with nanobumps and investigate their biosensing in comparison with the low-roughness (LR) counterparts. The HR metasurfaces demonstrate the surface sensitivity of multilayer polyelectrolyte molecules, which is 57.0% higher than the LR ones. The HR metasurfaces also illuminate higher immunoassay sensitivity to multiple lung cancer biomarkers, including carcinoembryonic antigen, neuron-specific enolase and cytokeratin fragment 21-1. The highest increasement of tumor marker sensitivity is up to 71.4%. The biosensing enhancement is attributed to the introduction of gold nanobumps on metasurfaces, which provides more hot-spot regions, higher localized near-field intensity and better optical impedance matching. Furthermore, the biosensing of HR metasurfaces effectively covers the threshold values of tumor markers for early lung cancer diagnosis, and is used for the detection of clinical serum samples. The testing deviation is less than 4% compared with commercial immunoassay, which implies promising applications on medical examinations. Our research provides a scientific guide to surface roughness engineering for plasmonic metasensing in the future point-of-care testing.

Affinity Exploration of SARS-CoV-2 RBD Variants to mAb-Functionalized Plasmonic Metasurfaces for Label-Free Immunoassay Boosting

Plasmonic metasurfaces (PMs) functionalized with the monoclonal antibody (mAb) are promising biophotonic sensors for biomolecular interaction analysis and convenient immunoassay of various biomarkers, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. Previous PM biosensing suffers from the slow affinity detection rate and lack of sufficient immunoassay studies on various SARS-CoV-2 variants. Here, we develop a high-efficiency affinity testing method based on label-free PM sensors with mAbs and demonstrate their binding characteristics to 12 spike receptor binding domain (RBD) variants of SARS-CoV-2. In addition to the research of plasmonic near-field influence on surface biomolecule sensing, we provide a comprehensive report about the Langmuir binding equilibrium of molecular kinetics between 12 SARS-CoV-2 RBD variants and mAb-functionalized PMs, which plays a crucial role in label-free immunosensing. A high-affinity mAb can be combined with the highly sensitive propagating plasmonic mode to boost the detection of SARS-CoV-2 variants. Owing to a better understanding of molecular dynamics on PMs, we develop an ultrasensitive biosensor of the SARS-CoV-2 Omicron variant. The experiments show great distinguishment of P < 0.0001 from respiratory diseases induced by other viruses, and the limit of detection is 2 orders smaller than the commercial colloidal gold immunoassay. Our study shows the label-free biosensing by low-cost wafer-scale PMs, which will provide essential information on biomolecular interaction and facilitate high-precision point-of-care testing for emerging SARS-CoV-2 variants in the future.

Sensitive and Specific Detection of Carcinoembryonic Antigens Using Toroidal Metamaterial Biosensors Integrated with Functionalized Gold Nanoparticles

Carcinoembryonic antigen (CEA) is a biomarker that is highly expressed in cancer patients. Label-free, highly sensitive, and specific detection of CEA biomarkers can therefore greatly aid in the early detection and screening of cancer. This study presents a toroidal metamaterial biosensor integrated with functionalized gold nanoparticles (AuNPs) that demonstrated highly sensitive and specific detection of CEA using terahertz (THz) time-domain spectroscopy. In the biosensor, a closed-loop magnetic field formed an electrical confinement, resulting in a high sensitivity (287.8 GHz/RIU) and an ultrahigh quality factor (15.04). In addition, the integrated AuNPs with high refractive indices significantly enhanced the sensing performance of the biosensor. To explore the quantitative and qualitative detection of CEA, CEA biomarkers with various concentrations and four types of proteins were measured by the designed biosensor, achieving a limit of detection of 0.17 ng and high specificity. Even more significant, the proposed AuNP-integrated THz toroidal metamaterial biosensor demonstrates exceptional potential for use in technologies for cancer diagnosis and monitoring.