Enhanced detection sensitivity of carcinoembryonic antigen on a plasmonic nanoimmunosensor by transmission grating-based total internal reflection scattering microscopy

Bimetallic Coordination Polymers: Synthesis and Applications in Biosensing and Biomedicine

Bimetallic coordination polymers (CPs) have two different metal ions as connecting nodes in their polymer structure. The synthesis methods of bimetallic CPs are mainly categorized into the one-pot method and post-synthesis modifications according to various needs. Compared with monometallic CPs, bimetallic CPs have synergistic effects and excellent properties, such as higher gas adsorption rate, more efficient catalytic properties, stronger luminescent properties, and more stable loading platforms, which have been widely applied in the fields of gas adsorption, catalysis, energy storage as well as conversion, and biosensing. In recent years, the study of bimetallic CPs synergized with cancer drugs and functional nanomaterials for the therapy of cancer has increasingly attracted the attention of scientists. This review presents the research progress of bimetallic CPs in biosensing and biomedicine in the last five years and provides a perspective for their future development.

Impedimetric aptasensor based on zirconium-cobalt metal-organic framework for detection of carcinoembryonic antigen

A zirconium-cobalt metal-organic framework (ZrCo-MOF) was prepared and used as sensing material to fabricate an aptasensor for trace detection of carcinoembryonic antigen (CEA). The ZrCo-MOF integrates the 3D porous structure and abundant defects of the MOF framework, the catalytic activity and inherent redox behavior of Co, and high stability of Zr-MOF, providing abundant active sites to effectively anchor aptamers. As a result, the ZrCo-MOF-based aptasensor shows high sensitivity to detect CEA via specific recognition between aptamer and CEA, as well as the formation of aptamer-CEA complex. A detection limit of 0.35 fg·mL^-1 was deduced from the electrochemical impedance spectroscopy within a wide linear range of 0.001-100 pg·mL^-1 for CEA, which was substantially lower than those of most reported CEA biosensors. The ZrCo-MOF-based aptasensor also shows good selectivity, reproducibility, regenerability, stability, and applicability for human serum sample. Therefore, the developed ZrCo-MOF-based aptasensor will be promising for ultrasensitive detection of biomarkers and the early diagnosis of cancer. This work presents a novel electrochemical aptasensor for the trace detection of carcinoembryonic antigen (CEA) based on a zirconium-cobalt metal-organic framework (ZrCo-MOF), which shows low detection limit of 0.35 fg·mL^-1, high selectivity as well as good reproducibility, regenerability, stability, and applicability. The result provides a promising approach to detect the cancer biomarkers in an early age.

Ultrasensitive Hypoxia Sensing at the Single-Molecule Level via Super-Resolution Quantum Dot-Linked Immunosandwich Assay

Activated hypoxia-inducible factor-1alpha (HIF-1α) plays an important role in the adaptive response of tumor cells to oxygen changes through the transcriptional activation of genes that regulate important biological processes required for tumor survival and progression. In this study, we developed an ultrasensitive hypoxia sensor based on read-out with quantum dots on a gold nanodisc (quantum dot-linked immunosandwich assay, QLISA) with excellent selectivity for HIF-1α. The immunoassay platform was established by comparing the immune response results using Qdot525 as a detection nanoprobe instead of a fluorescent dye (Alexa488) (fluorescent-linked immunosandwich assay, FLISA). In addition, using three-dimensional total internal reflection fluorescence microscopy, the platform was optically sectioned along the z-axis at 10 nm intervals to compare the height difference between the nanodisc and the nanoprobe following the QLISA and FLISA procedures and to localize the target location. Here, the super-resolution QLISA (srQLISA)-based hypoxia sensor exhibited high accuracy and precision for the detection of HIF-1α-extracted samples in cancer spheroids compared with the super-resolution FLISA (srFLISA) method. The developed nanobiosensor method demonstrated a wide dynamic linear detection range of 32.2 zM-8.0 pM with a limit of detection of 16 zM under optimal experimental conditions for HIF-1α, an approximate 10⁶-fold enhanced detection sensitivity compared with the conventional enzyme-linked immunosorbent assay method based on absorbance. The detection of HIF-1α using the newly developed srQLISA sensor allows for independently predicting tumor progression and early cancer onset increases in the microvasculature density of tumor lesions.

Aptamer-based biosensor for detecting carcinoembryonic antigen

Carcinoembryonic antigen (CEA), as one of the common tumor markers, is a human glycoprotein involved in cell adhesion and is expressed during human fetal development. Since the birth of human, CEA expression is largely inhibited, with only low levels in the plasma of healthy adults. Generally, CEA will overexpressed in many cancers, including gastric, breast, ovarian, lung, and pancreatic cancers, especially colorectal cancer. As one of the important tumor markers, the detection of CEA has great significance in differential diagnosis, condition monitoring and therapeutic evaluation of diseases. Conventional CEA testing typically uses immunoassay methods. However, immunoassay methods require complex and expensive instruments and professional personnel to operate. Moreover, radioactive element may cause certain damage to the human body, which limits their wide application. In the past few years, biosensors, especially aptamer-based biosensors, have attracted extensive attention due to their high sensitivity, good selectivity, high accuracy, fast response and low cost. This review briefly classifies and describes the advance in optical and electrochemical aptamer biosensors for CEA detection, also explains and compares their advantages and disadvantages.

Supersensitive Detection of the Norovirus Immunoplasmon by 3D Total Internal Reflection Scattering Defocus Microscopy with Wavelength-Dependent Transmission Grating

Norovirus (NoV) is a major foodborne pathogen, and even low levels of virus can cause infection and gastroenteritis. We developed a supersensitive NoV sensor that detects NoV group-I capsid protein (NoVP) via three-dimensional (3D) total internal reflection scattering defocus microscopy (TIRSDM) with wavelength-dependent transmission grating (TG). The combination of evanescent wave scattering and TG significantly enhanced the detection sensitivity and selectivity of NoVP in first-order spectral images (n = +1) by minimizing spectroscopic interference and background noise. In particular, wavelength-dependent 3D defocused TG imaging (3D TG-TIRSDM) separated silver nanotag and gold nanoplate signals on a NoVP immunoplasmon chip along the x, y, and z coordinates simultaneously. Additionally, the use of wavelength-dependent TG increased the spectral resolution by 5-fold along the xy-axis and 1.4-fold along the z-axis compared to conventional 3D TIRSDM at the subdiffraction limit. The NoVP sensor exhibited a lower limit of detection of 820 yM, which is 29 000 times better than the previous potentiometer method, and a wide dynamic detection range of 820 yM to 92.45 pM (R = 0.9801). This new method could be applied to detect various pathogenic viruses during the initial stage of infection.

A Single-Molecule Homogeneous Immunoassay by Counting Spatially "Overlapping" Two-Color Quantum Dots with Wide-Field Fluorescence Microscopy

We developed a single-molecule homogeneous immunoassay by counting spatially "overlapping" two-color quantum dots (QD) under a wide-field fluorescence microscope. QD 655 with red fluorescence and QD 565 with green fluorescence were modified with capture and detection antibodies, respectively. A capture antibody-modified QD 655 and a detection antibody-modified QD 565 were conjugated by a corresponding antigen molecule to form a "sandwich" immunocomplex. The conjugated QD 655 could not be distinguished from the conjugated QD 565 by fluorescent microscopy because the distance between them was smaller than the resolution of an optical microscope (approximately 200 nm). The immunocomplex color became yellow because of the spatial "overlap" of the red and green fluorescence. The number of the yellow spots was equal to the number of immunocomplex molecules, while the concentration of the antigen was related to the ratio of the yellow dots to the red dots. The successful quantification of two model proteins in the human plasma, namely, alpha-fetoprotein and carcinoembryonic antigen, demonstrated the accuracy and reliability of our approach.