Polycytosine DNA Electric-Current-Generated Immunosensor for Electrochemical Detection of Human Epidermal Growth Factor Receptor 2 (HER2)

Electrochemical Detection of Circulating Tumor Cells Based on DNA Generated Electrochemical Current and Rolling Circle Amplification

Circulating tumor cells (CTCs) are important indicators for tumor diagnosis and tumor metastasis. However, the extremely low levels of CTCs in peripheral blood challenges the precise detection of CTCs. Herein, we report DNA generated electrochemical current combined with rolling circle amplification (RCA) as well as magnetic nanospheres for highly efficient magnetic capture and ultrasensitive detection of CTCs. The antiepithelial cell adhesion molecule (EpCAM) antibody-modified magnetic nanospheres were used to capture and enrich CTCs. The following binding of an aptamer onto the CTC surface and the subsequent RCA assembled a significant amount of DNA molecules onto the electrode. The reaction of the DNA molecules with molybdate can then form redox molybdophosphate and produce an electrochemical current. Using the breast cancer cell MCF-7 as a model, the sensor displays good performances toward detection of MCF-7 that was spiked into peripheral blood. The signal amplification strategy integrated with a magnetic nanosphere platform exhibits good performance in the efficient capture and detection of CTCs, which may find wide potential in cancer diagnostics and therapeutics.

Photoelectrochemical detection of breast cancer biomarker based on hexagonal carbon nitride tubes

Photoelectrochemical (PEC) sensor for sensitive detection of breast cancer biomarker human epidermal growth factor receptor 2 (HER2) utilizing hexagonal carbon nitride tubes (HCNT) as photoactive material is reported. The detection is based on suppression of the PEC current intensity of the sensor. HCNT were synthesized via a facile hydrothermal method with large specific surface area and low electron-hole recombination. Au nanoparticles (AuNPs) were deposited onto the surface of the HCNT, which enhanced the photocurrent intensity of the HCNT by one time. For HER2 detection, peptide specific to HER2 was immobilized on the AuNPs surface for capturing HER2 molecules. The following binding of HER2 with HER2 aptamer and the reaction of phosphate groups on aptamer with molybdate can form molybdophosphate precipitate, which sticks to the surface of HCNT and impedes electron transport. Thus, photocurrent intensity of the sensor was suppressed. Under optimal conditions, the linear relationship between the PEC intensity and the logarithm of HER2 concentration was from 0.5 to 1 ng mL^-1 with low limit of detection (LOD) of 0.08 pg mL^-1. Furthermore, the PEC sensor also displayed capability for detecting HER2 in human serum samples. This PEC sensor signal detection strategy can be easily adapted to other PEC sensors involving DNA and find wide applications. Graphical abstract.

An Electrochemical Sandwich Immunosensor for the Detection of HER2 using Antibody-Conjugated PbS Quantum Dot as a label

A facile electrochemical sandwich immunosensor for the detection of a breast cancer biomarker, the human epidermal growth factor receptor 2 (HER2), was designed, using lead sulfide quantum dots-conjugated secondary HER2 antibody (Ab2-PbS QDs) as a label. Using Ab2-PbS QDs in the development of electrochemical immunoassays leads to many advantages such as straightforward synthesis and well-defined stripping signal of Pb(II) through acid dissolution, which in turn yields better sensing performance for the sandwiched immunosensor. In the bioconjugation of PbS QDs, the available amine and hydroxyl groups from secondary anti-HER2 and capped PbS QDs were bound covalently together via carbonyldiimidazole (CDI) acting as a linker. In order to quantify the biomarker, SWV signal was obtained, where the Pb²⁺ ions after acid dissolution in HCl was detected. The plated mercury film SPCE was also detected in situ. Under optimal conditions, HER2 was detected in a linear range from 1-100 ng/mL with a limit of detection of 0.28 ng/mL. The measures of satisfactory recoveries were 91.3% to 104.3% for the spiked samples, displaying high selectivity. Therefore, this method can be applied to determine HER2 in human serum.

Advances in HER2 testing

HER2-positive breast cancer is a particularly aggressive type of breast cancer. Indication of HER2 positivity is essential for its treatment. In addition to a few FDA-approved methods such as immunohistochemical (IHC) detection of HER2 protein expression and in situ hybridization (ISH) assessment of HER2 gene amplification, several novel methods have been developed for HER2 testing in recent years. This chapter provides an overview of HER2 testing with emphasis on those new methods.

Au@Pt nanodendrites enhanced multimodal enzyme-linked immunosorbent assay

Single modal enzyme-linked immunosorbent assay (ELISA) covering colorimetric, fluorescence, and chemiluminescence techniques has been widely reported in recent years, whereas the combination of multiple signal channels in one immunosensing platform still faces huge challenges. Multimodal imaging will provide more comprehensive and precise diagnostic information by the combination of two or more imaging modalities. Inspired by this concept, we established a new kind of multimodal enzyme-linked immunosorbent assay (M-ELISA) based on the unique properties of Au@Pt nanodendrites. As a proof-of-concept demonstration, cardiac troponin I (cTnI) has been chosen as a model biomarker. Owing to the excellent photothermal effect and intrinsic peroxidase-like activity of Au@Pt nanodendrites, the concentration of cTnI can be quantificationally reflected by photothermal immunoassay, colorimetric immunoassay and ratiometric fluorescence immunoassay simultaneously. This developed M-ELISA demonstrated the good consistency with the chemiluminescence immunoassay method in clinical diagnosis for real serum samples.

Aptamer based determination of the cancer biomarker HER2 by using phosphate-functionalized MnO2 nanosheets as the electrochemical probe

The authors report a sensitive electrochemical aptamer-based assay for the cancer biomarker human epidermal growth factor receptor-2 (HER2). It is based on the use of MnO₂ nanosheets that were functionalized with phosphate and a HER2 binding aptamer and serve as the electrochemical probe. The assay follows a sandwich protocol. A peptide that can specifically recognize HER2 was immobilized on a gold electrode for the capture of HER2. Then, the functionalized MnO₂ nanosheets were linked to the electrode via the binding between HER2 and HER2 aptamer on the MnO₂ nanosheets. The reaction of phosphate and aptamer on the MnO₂ nanosheets with molybdate leads to the formation of redox-active molybdophosphate. This results in dual signal amplification. The generated electrochemical current was measured at 0.22 V (vs. Ag/AgCl). The assay allows HER2 to be determined in the 0.1 to 500 pg·mL^-1 concentration range, and the detection limit is as low as 0.05 pg·mL^-1. The assay was successfully applied for the detection of HER2 in spiked human serum samples. Graphical abstract Electrochemical detection of breast cancer biomarker human epidermal growth factor receptor-2 (HER2) is reported utilizing phosphate ions and aptamer functionalized MnO₂ nanosheet as probe.

Bimetallic ZrHf-based metal-organic framework embedded with carbon dots: Ultra-sensitive platform for early diagnosis of HER2 and HER2-overexpressed living cancer cells

We report here a new bimetallic ZrHf metal-organic framework (ZrHf-MOF) embedded with abundant carbon dots (CDs) (denoted as CDs@ZrHf-MOF), which exhibits strong fluorescence and rich-amino-functionalization. The CDs@ZrHf-MOF can be applied as the scaffold for anchoring aptamer strands to determine human epidermal growth factor receptor-2 (HER2) and living HER2-overexpressed MCF-7 cells. The basic characterizations reveal that the CDs are embedded within the interior cavities of ZrHf-MOF without varying the nanostructure, leading to good biocompatibility, strong fluorescence, and high electrochemical activity of CDs@ZrHf-MOF. As compared with the pristine ZrHf-MOF, the CDs@ZrHf-MOF-based electrochemical aptasensor displays better sensing performances toward both HER-2 and MCF-7 cells, giving an extremely low detection limit of 19 fg mL^-1 (HER2 concentration range: 0.001-10 ng mL^-1) and 23 cell mL^-1 (cell concentration range: 1 × 10²~1 × 10⁵ cell mL^-1), with good selectivity, stability, reproducibility, and acceptable applicability. The proposed strategy for developing CDs@ZrHf-MOF-based aptasensor is promising for the early and sensitive detection of cancer markers and living cancer cells.

Electrochemical determination of the activity and inhibition of telomerase based on the interaction of DNA with molybdate

An ultrasensitive electrochemical sensor is described for the determination of the activity of telomerase. It is based on a DNA-generated current that is due to the reaction of the phosphate groups on DNA with molybdate to form a redox-active molybdophosphate. A telomerase substrate primer was first immobilized on a gold electrode. In the presence of telomerase and deoxyribonucleoside triphosphates (dNTPs), the primer can be extended with repetitive nucleotide sequences (TTAGGG). The subsequent reaction of the sensor with molybdate results in the enhancement of electrochemical current intensity due to an increased amount of nucleotides on the electrode. Sensitivity can be further improved by introducing a hairpin probe that partially hybridizes with the repetitive TTAGGG sequence and further enhances the amount of DNA on the electrode. The biosensor, best operated at 0.2 V (vs. Ag/AgCl) shows a linear response to telomerase activity from 1×10² to 10⁷ Hela cells mL^-1. The assay was applied to the detection of telomerase activity in HeLa cancer cells treated with the anticancer drug epigallocatechin gallate, and the results indicate that it holds great potential in anticancer drug screening. Graphical abstract Schematic presentation of an ultrasensitive electrochemical sensor for the determination of telomerase activity based on DNA generated electrochemical current. dNTPs in the scheme represents deoxyribonucleoside triphosphates.

A dual-aptamer-based biosensor for specific detection of breast cancer biomarker HER2 via flower-like nanozymes and DNA nanostructures

A dual-aptamer electrochemical biosensor based on flower-like nanozymes and DNA nanostructures was fabricated for detection of breast cancer biomarker HER2.

Two-dimensional porphyrin-based covalent organic framework: A novel platform for sensitive epidermal growth factor receptor and living cancer cell detection

A porphyrin-based covalent organic framework (denoted as p-COF) was synthesized by a simple oil-bath method and exploited as a novel sensing layer for immobilizing epidermal growth factor receptor (EGFR)-targeting aptamer strands to detect trace EGFR and living michigan cancer foundation-7 (MCF-7) cells for the first time. p-COF presented a nanosheet-like structure, large cavities, rich nitrogen-bearing groups, high electrochemical activity, excellent bioaffinity, low toxicity, and good stability in aqueous solution; the microstructural features of this material enabled strong immobilization of the aptamer strands. Interactions between the aptamer strands and EGFR significantly changed the electrochemical signals of the modified electrode due to the formation of an aptamer-EGFR complex. The p-COF-based aptasensor exhibited an extremely low detection limit (LOD) of 5.64 fg·mL^-1 obtained from differential pulse voltammetry and 7.54 fg·mL^-1 originated from electrochemical impedance spectroscopy with a broad linear detection range of 0.05-100 pg·mL^-1 of the EGFR concentration. When detecting living MCF-7 cells, the p-COF-based aptasensor showed an LOD of 61 cell·mL^-1 with a linear detection range of 500 × 10⁵ cell·mL^-1. The fabricated aptasensor exhibited high selectivity, good stability, reproducibility, acceptable recyclability, and favorable applicability in human serum samples. We believe that the developed p-COF-based aptasensor is a potential candidate for the sensitive detection of target cancer markers or living cells.