As a kind of most important cancer biomarker, exosomes are getting more frequently investigated in cancer diagnosis. In this study, we proposed an SERS-based method for the screening and simultaneous multiple detection of exosomes using magnetic substrates and SERS probes. Specifically, the capturing substrates are achieved using gold shell magnetic nanobeads modified by aptamers, which can capture most kinds of exosomes by recognizing the generic surface protein CD63. Moreover, the SERS probes are made of gold nanoparticles decorated with a Raman reporter and a specific aptamer for targeting exosomes. Further, for the simultaneous detection of multiple kinds of exosomes, three kinds of SERS probes were designed using different SERS reporters. While detecting specific kinds of exosomes, the capturing substrates were mixed with these three kinds of SERS probes. When the target exosome is present, an apta-immunocomplex can be formed among the target exosomes, the substrate, and the corresponding kind of SERS probes, and the other non-specific SERS probes remain in the suspension. Hence, an SERS signal with a decreased intensity will be detected in the supernatant, indicating the presence of the target exosomes. Finally, this detection method has also been successfully employed for the detection of exosomes in real blood samples; this proves that the proposed SERS-based method is a promising tool for clinical cancer screening based on exosomes.
A surface-enhanced
Raman scattering (SERS) aptasensor based on a hydrophobic assembled
nanoacorn (HANA) was developed with improved reproducibility and reduced
nonspecific binding effect. In the fabrication process, a hexagonal-packed
gold film over nanosphere (AuFON) arrays was first obtained and used
as a hydrophobic plasmonic substrate. Then, a uniform sub-3 nm molecular
spacer array (containing Raman reporters) was prepared by patterning
nanometric hydrophilic ultrathin patches onto the hydrophobic AuFON,
in which the hydrophilic thin layer is composed of polymers and aptamers.
During the sensing process, the HANA aptasensor smartly impedes the
adsorption of SERS probes as Au@Ag nanocubes (Au@Ag NCs) in the absence
of targets. In the presence of targets, the displacement of aptamers
occurs due to the specific interaction between the targets and the
aptamers, and the Au@Ag NCs can be assembled onto the hydrophilic
patches on AuFON through electrostatic interactions with polymers.
Thus, SERS signals of reporter molecules inside the spacer can be
dramatically enhanced due to the formation of a nanoparticle-on-mirror
(NPoM) array. In such a SERS aptasensor, the well-ordered distribution
of SERS probes ensures excellent repeatability, while the precise
subnanometer junctions guarantee high sensitivity. More importantly,
since the hydrophobic surface can greatly reduce nonspecific adsorption,
the tedious process of nonspecific blocking that is employed in traditional
biosensors is no longer needed. Using such a SERS HANA platform, human
epidermal growth factor receptor 2 (HER2) and three exosomal proteins
were analyzed with high sensitivity and good reproducibility (RSD <
7%) in whole-blood samples.
The interfacial fluid thickness (IFT) concept was used to develop a harmonic-mean refractive index gradient magnitude threshold to retrieve the high refractive index gradient regions of an aerodynamically heated window. The retrieved high-gradient regions were used to reconstruct the refractive index field of the window. The numerical three-dimensional optical distortion evaluation was conducted for both the reconstructed and the original refractive index fields of the window using the ray-tracing program based on a recursive algorithm. Wave aberration results show that the methodology based on the IFT concept reduces the refractive index information required to capture the essential optical distortion of the window. The method can also be used for numerically evaluating the optical distortion of the window.
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