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Plasmonic sensing has a great potential in the portable detection of human tumor markers, among which the carcinoembryonic antigen (CEA) is one of the most widely used in clinical medicine. Traditional plasmonic and non-plasmonic methods for CEA biosensing are still not suitable for the fast developing era of Internet of things. In this study, we build up a cost-effective plasmonic immunochip platform for rapid portable detection of CEA by combining soft nanoimprint lithography, microfluidics, antibody functionalization, and mobile fiber spectrometry. The plasmonic gold nanocave array enables stable surface functionality, high sensitivity, and simple reflective measuring configuration in the visible range. The rapid quantitative CEA sensing is implemented by a label-free scheme, and the detection capability for the concentration of less than 5 ng/ml is achieved in clinical experiments, which is much lower than the CEA cancer diagnosis threshold of 20 ng/ml and absolutely sufficient for medical applications. Clinical tests of the chip on detecting human serums demonstrate good agreement with conventional medical examinations and great advantages on simultaneous multichannel detections for high-throughput and multi-marker biosensing. Our platform provides promising opportunities on low-cost and compact medical devices and systems with rapid and sensitive tumor detection for point-of-care diagnosis and mobile healthcare.

Metasurfaces are planar or 2D forms of metamaterials made up of arrays of antennas with a subwavelength thickness. They have been rapidly developed in the recent years due to their ability to manipulate light–matter interaction in both linear and non‐linear regimes at the nanoscale. Various metasurfaces display remarkable optical features, such as acute resonance, significant near‐field enhancement, and suitable capacity to support electric and magnetic modes, on account of the strong light–matter interaction and the low optical loss. Due to these important properties, they can be used in several advanced optoelectronic applications, like surface‐enhanced spectroscopy, photocatalysis, and sensing. This review reports on the recent progress of metamaterials and metasurfaces in molecular optical sensors. The principles that govern plasmonic and dielectric metasurfaces along with their features are outlined, supported by numerous examples. Then, the factors that result in a high Q‐factor are presented in order to show that metamaterials and metasurfaces can be used for label‐free sensing in a variety of detection mechanisms, including surface‐enhanced spectroscopy, refractometric sensing, and surface‐enhanced thermal emission spectroscopy via infrared absorption and Raman scattering, as well as chiral sensing. Finally, the challenges for future development are outlined. [ABSTRACT FROM AUTHOR]

The use of plasmonic metasurface for sensing has great potential on label-free detection of human tumor markers, which could benefit clinical examination. In this work, we adopt nanoimprint and plasma etching to optimize the nanofabrication for low-cost flexible plasmonic metasurface sensors with gold nanobump arrays, which enable facile surface bio-functionality, high sensitivity and simple optical measurement in the visible range. A high bulk refractive index sensitivity of 454.4 nm/RIU is achieved for the prototype plasmonic metasurface sensors at the wavelengths from 620 nm to 720 nm. The rapid quantitative tumor marker sensing of carcinoembryonic antigen in human serum samples from less than 10 ng/mL to more than 87 ng/mL is achieved, which demonstrates good agreement with the conventional chemiluminescence immunoassay system and sufficiently covers the threshold tumor marker concentration of 20 ng/mL for early cancer prediction. Our method is capable of low-cost high-throughput manufacturing for flexible lightweight plasmonic metasurface sensors, which will facilitate wide applications on portable biomedical sensing devices for future point-of-care diagnosis and mobile healthcare. • Large-scale metasurfaces on lightweight flexible substrates for portable biosensing. • Cost-effective fabrication for mass production by soft nanoimprint lithography. • The entire gold encapsulation benefits the process of antibody functionalization. • Low-cost and compact reflection-type sensing system in the visible range. • High sensitivity for detecting tumor markers, which is competitive with the conventional immunoassay system. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • The gold nanobumps of plasmonic metasurfaces enhance the near-field intensity and provide much more hot-spot regions. • The sensitivity enhancement of tumor marker by increasing metasurface roughness is up to 71.4%. • The serum tests of high-roughness metasurfaces have the deviation of lower than 4% to commercial immunoassay. [ABSTRACT FROM AUTHOR]

• The low-cost metasurface of aluminum shows exceptional biosensing performance. • The metasurface of aluminum demonstrates better surface sensitivity than gold. • The aluminum metasurface achieves a limit of biomolecular detection of 1 pg/mL. Aluminum has recently attracted significant interest as a promising alternative material to noble metals for plasmonic metasurface biosensing, but it suffers from surface oxidation and higher visible-light loss, which is usually believed to limit its capability of sensing. We report here that the large-area flexible passivated Al nanopillar metasurface shows better bulk and surface sensing performance than Au nanopillar metasurface. Compared to the Au metasurface, the existance of superficial alumina layer protects the Al metasurface from further oxidation and maintains the high surface sensitivity. In the test for the antibody of bovine serum albumin, the Al-based metasurface demonstrates a much higher sensitivity by two orders of magnitude versus the Au counterpart. Its detection of limit is as low as 1 pg/mL, which implies a great potential for clinical diagnosis. Our study paves the way for the use of Al metasurface in low-cost high-performance biosensing of mobile healthcare. [ABSTRACT FROM AUTHOR]