Metal-mediated Fe3O4@polydopamine-aptamer capture nanoprobe coupling multifunctional MXene@Au@Pt nanozyme for direct and portable photothermal analysis of circulating breast cancer cells

Breast cancer (BC) is the most common cancer in the world and circulating tumor cells (CTCs) are reliable biomarkers for early breast cancer diagnosis in a non-invasive manner. However, effective isolation and sensitive detection of BC-CTCs by portable devices in human blood samples are extremely challenging. Herein, we proposed a highly sensitive and portable photothermal cytosensor for direct capture and quantification of BC-CTCs. To achieve efficient isolation of BC-CTCs, aptamer functionalized Fe₃O₄@PDA nanoprobe was facilely prepared through Ca²⁺-mediated DNA adsorption. To further detect the captured BC-CTCs with high sensitivity, multifunctional two-dimensional Ti₃C₂@Au@Pt nanozyme was synthesized, which not only possessed superior photothermal effect but also exhibited high peroxidase-like activity for catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) to produce TMB oxide (oxTMB) with a strong photothermal characteristic, combining with Ti₃C₂@Au@Pt to synergistically amplify the temperature signal. Moreover, numerous Ti₃C₂@Au@Pt nanocomposites would be selectively attained on the BC-CTCs surface through multi-aptamer recognition and binding strategy, which further enhanced the specificity and facilitated signal amplification. Therefore, direct separation and highly sensitive detection of BC-CTCs was successfully achieved in human blood samples. More significantly, the controlled release of the captured BC-CTCs without affecting cell viability could be straightforwardly realized by a simple strand displacement reaction. Thus, with the distinct features of portability, high sensitivity, and easy operation, the current method holds great promise for early diagnosis of breast cancer.

A simple and sensitive electrochemical biosensor for circulating tumor cell determination based on dual-toehold accelerated catalytic hairpin assembly

Tumor cells in blood circulation (CTCs) are vital biomarkers for noninvasive cancer diagnosis. We developed a simple and sensitive electrochemical biosensor based on dual-toehold accelerated catalytic hairpin assembly (DCHA) to distinguish CTCs from blood cells. In the presence of CTCs, the aptamer probe initiates the DCHA process, which produces amplified electrochemical signals. Compared with conventional catalytic hairpin assembly (CHA), the proposed DCHA showed high sensitivity, which led to a broader working range of 10-1000 cells mL^-1 with a limit of detection of 4 cells mL^-1. Furthermore, our method exhibited an excellent capability of distinguishing malignant breast cancers from healthy people, with a sensitivity of 97.4%. In summary, we have established an enzyme-free, easy-to-operate, and nondisruptive method for detecting circulating tumor cells in blood circulation based on the DCHA strategy. Its versatility and simplicity will make it more widely used in clinical diagnosis and biomedical research.

Fabrication of a Polyvalent Aptamer Network on an Electrode Surface for Capture and Analysis of Circulating Tumor Cells

Capture and analysis of circulating tumor cells (CTCs) from complex matrixes is pivotal for the prediction of cancer metastasis and personalized treatment of cancer. Herein, we propose a strategy for CTC capture by design and fabrication of a polyvalent aptamer network on an electrode surface, which can be further used for the sensitive analysis of CTCs. In our design, the polyvalent aptamer network, which is constructed via a rolling circle amplification reaction, can significantly enhance the cell-binding abilities. Meanwhile, tetrahedral DNA structures previously assembled on the electrode surface will promote the spatial orientation and reduce the steric hindrance effect of the cell capture, thus improving the cell capture efficiency. Importantly, a detectable electrochemical signal can be obtained without additional signal probes by means of target-induced allostery of the DNA hairpin structures. Further studies reveal that the electrochemical response is proportional to the logarithm of the CTC abundance ranging from 10² to 5 × 10⁴ cell mL^-1 with a low limit of detection of 23 cell mL^-1. Moreover, the proposed capture strategy exhibits excellent stability and anti-interference in human whole blood, indicating its promising potential in clinical diagnosis.

A review of enrichment methods for circulating tumor cells: from single modality to hybrid modality

Circulating tumor cell (CTC) analysis as a liquid biopsy can be used for early diagnosis of cancer, evaluating cancer progression, and assessing treatment efficacy. The enrichment of CTCs from patient blood is important for CTC analysis due to the extreme rarity of CTCs. This paper updates recent advances in CTC enrichment methods. We first review single-modality methods, including biophysical and biochemical methods. Hybrid-modality methods, combining at least two single-modality methods, are gaining increasing popularity for their improved performance. Then this paper reviews hybrid-modality methods, which are categorized into integrated and sequenced hybrid-modality methods. The state of the art indicates that the CTC capture efficiencies of integrated hybrid-modality methods can reach 85% or higher by taking advantage of the superimposed and enhanced capture effects from multiple single-modality methods. Moreover, a hybrid method integrating biophysical with biochemical methods is characterized by both high processing rate and high specificity.

The isolation and analysis of fetal nucleated red blood cells using multifunctional microbeads with a nanostructured coating toward early noninvasive prenatal diagnostics

Prenatal diagnostics holds great significance for pregnant women desiring healthy babies. Fetal nucleated red blood cells (fNRBCs), bearing the complete genome of the fetus, have been regarded as an important biomarker for noninvasive prenatal diagnostics (NIPD). The high-performance detection and enrichment of fNRBCs from maternal blood, especially during early pregnancy, is urgently needed for NIPD, which, unfortunately, remains a big challenge for early-pregnancy fNRBC isolation. In this study, we developed an innovative platform based on silica microbeads for fNRBC isolation and release in early pregnancy. Microbeads were coated with self-assembled MnO₂ nanoparticles (SiO₂@MnO₂) and then modified with a specific antibody. Benefiting from the three-dimensional nanostructure of the MnO₂ nanoparticles, the isolation efficiency of the fNRBCs was enhanced. Subsequently, fNRBCs were released via dissolving the MnO₂-nanoparticle coating using oxalic acid. We successfully isolated fNRBCs from the maternal peripheral blood samples of 20 pregnant women in the early pregnancy period, ranging from 41 to 62 gestational days. More importantly, the fetal origin of isolated cells was confirmed via fluorescent in situ hybridization and short tandem repeat analysis. This platform based on SiO₂@MnO₂ microbeads has verified the existence of fNRBCs in early-pregnancy maternal blood and is a promising approach for NIPD in early pregnancy.

Direct Analysis of Rare Circulating Tumor Cells in Whole Blood Based on Their Controlled Capture and Release on Electrode Surface

The development of a simple, sensitive, and effective method for the analysis of circulating tumor cells (CTCs) is essential for cancer diagnosis and metastasis prediction. In this work, we have proposed an enzyme-free electrochemical method for specific capture, sensitive quantification, and efficient release of CTCs. To achieve this, the specific interaction between CTCs and the corresponding aptamer designed to be located in the identification probe (IP) will unfold the hairpin structure of IP. Consequently, IP will initiate a hybridization reaction to produce a duplex, which will further trigger the hybridization chain reaction (HCR) process to form a composite product of CTCs and double-stranded DNA polymers. Therefore, a significantly amplified signal readout can be obtained. Moreover, the composite product can be brought to the electrode surface by tetrahedral DNA nanostructures to achieve the purpose of capturing and quantifying CTCs. More significantly, these captured CTCs can be controlled released without compromising cell viability via a simple strand displacement reaction. Taking the breast cancer cell MCF-7 as a representative, the newly developed approach led to an ultralow detection limit of 3 cells mL^-1, which is superior to several studies previously reported. The current method has also been demonstrated to analyze CTCs in human whole blood and hence revealed a great potential in the future.

Development and Application of an Immunocapture PCR Diagnostic Assay Based on the Monoclonal Antibody for the Detection of Shigella

Background:

Shigella is among the most important human pathogenic microorganisms, infecting both humans and nonhuman and causing clinically severe diarrhea. Shigella must be enriched before detection, which is time-consuming.

Objectives:

To develop a sensitive, rapid, and specific method for Shigella detection.

Materials and Methods:

Shigella was used as an antigen to generate monoclonal antibodies (mAbs). mAbs were screened via indirect enzyme-linked immunosorbent assay (ELISA) and western blot, and two mAbs were selected. The mAb A3 showed high affinity and specificity and was used to develop immune magnetic beads (IMBs) for Shigella enrichment. An immunocapture (IC)-PCR primer was designed from the ipaH gene, and IC-PCR was developed based on the IMBs and PCR.

Results:

This system shortened the Shigella detection time to 70 min. The sensitivity of the IC-PCR was 9 colony-forming units.mL^-1 in artificial milk. The accuracy of the IC-PCR was confirmed using 46 clinical samples collected from monkeys. The IC-PCR results were consistent with the serological and biochemical assays.

Conclusion:

The IC-PCR described herein accurately detected Shigella from milk samples, monkeys and can thus be used to complement classical detection methods.

Dopamine-functionalized hyaluronic acid microspheres for effective capture of CD44-overexpressing circulating tumor cells

As one of the biomarkers of liquid biopsy, circulating tumor cells (CTCs) provides important clinical information for cancer diagnosis. However, accurate separation and identification of CTCs remains a great deal of challenge. In present work, we developed novel dopamine-functionalized hyaluronic acid microspheres (HA-DA microspheres) to capture CD44-overexpressing CTCs. The dopamine was grafted onto the hyaluronic acid chain, which was polymerized and cross-linked by oxidation of the catechol groups. Afterwards, a facile microfluidic chip was designed and developed to fabricate the HA-DA microspheres with a diameter of about 45 μm. Our results showed that the CD44+ cells (i.e., HeLa, HepG2, A549, MCF-7 and DU-145 cells) could be selectively captured. Then a double-layer microfluidic filter (DLMF) was fabricated for dynamic isolation and detection of CTCs in blood samples. Many slit openings with 15 μm in height were designed to allow white blood cells to clear away, while the microspheres with CTCs were intercepted in the DLMF, which achieved effective separation of CTCs from blood cells. The approach exhibited high capture efficiency even at the cell density as low as 10 cells/mL. We believe the DLMF integrated with HA-DA microspheres could be a promising approach for isolation and detection of CD44-overexpressing CTCs, which is useful for prognosis and early metastasis of cancer patients.

In Situ-Generated Multivalent Aptamer Network for Efficient Capture and Sensitive Electrochemical Detection of Circulating Tumor Cells in Whole Blood

Monitoring circulating tumor cells (CTCs) in human blood can offer useful information for convenient metastasis diagnosis, prognosis, and treatment of cancers. However, it remains a substantial challenge to detect CTCs because of their particular scarcity in complex peripheral blood. Herein, we describe an in situ-generated multivalent aptamer network-modified electrode interface for efficiently capturing and sensitively detecting CTCs in whole blood by electrochemistry. Such an interface was fabricated via rolling circle amplification extension of the electrode-immobilized primer/circular DNA complexes for the yield of long ssDNA strands with many repeated aptamer segments, which could achieve efficient capture of rare CTCs in a multivalent cooperative manner. The antibody and horseradish peroxidase-functionalized gold nanoparticles further specifically associated with the surface-bound CTCs and generated electrocatalytically amplified current outputs for highly sensitive detection of CTCs with an attractive detection limit of five cells. Also, the multivalent aptamer network interface could successfully distinguish the target cells from other control cells and achieve CTC detection in whole blood, demonstrating its promising potential for monitoring different rare CTCs in human blood.

Highly specific and sensitive point-of-care detection of rare circulating tumor cells in whole blood via a dual recognition strategy

Despite the fact that the identification and detection of circulating tumor cells (CTCs) plays a critical role in cancer monitoring and diagnosis, it remains a major challenge to isolate and detect these cells, due to their extreme scarcity in peripheral blood. In this work, by coupling a dual recognition strategy and the commercial personal glucose meter, we established a point-of-care approach for detecting rare CTCs in whole blood with high sensitivity and selectivity. The antibody-conjugated magnetic beads lead to the capture and isolation of the CTCs while the enzyme- and second antibody-modified microspheres yield the signal for detection. Because of the dual recognition format, the developed method is highly selective, and a low detection limit of 7 cells can be realized as well, owing to the great signal amplification through the enzyme-loaded microbead labels. More importantly, the detection of CTCs in whole blood can be achieved in a point-of-care fashion with the using of the glucose meter transducer, offering our method a convenient and attractive alternative to traditional biopsy for the diagnosis of various cancers.

Recent advances in microfluidic methods in cancer liquid biopsy

Early cancer detection, its monitoring, and therapeutical prediction are highly valuable, though extremely challenging targets in oncology. Significant progress has been made recently, resulting in a group of devices and techniques that are now capable of successfully detecting, interpreting, and monitoring cancer biomarkers in body fluids. Precise information about malignancies can be obtained from liquid biopsies by isolating and analyzing circulating tumor cells (CTCs) or nucleic acids, tumor-derived vesicles or proteins, and metabolites. The current work provides a general overview of the latest on-chip technological developments for cancer liquid biopsy. Current challenges for their translation and their application in various clinical settings are discussed. Microfluidic solutions for each set of biomarkers are compared, and a global overview of the major trends and ongoing research challenges is given. A detailed analysis of the microfluidic isolation of CTCs with recent efforts that aimed at increasing purity and capture efficiency is provided as well. Although CTCs have been the focus of a vast microfluidic research effort as the key element for obtaining relevant information, important clinical insights can also be achieved from alternative biomarkers, such as classical protein biomarkers, exosomes, or circulating-free nucleic acids. Finally, while most work has been devoted to the analysis of blood-based biomarkers, we highlight the less explored potential of urine as an ideal source of molecular cancer biomarkers for point-of-care lab-on-chip devices.

Detection of Escherichia coli O157:H7 and Salmonella enterica serotype Typhimurium based on cell elongation induced by beta-lactam antibiotics

Pathogenic bacteria such as Shiga toxigenic Escherichia coli and Salmonella can cause severe food-borne diseases. Rapid and sensitive detection of these foodborne pathogens is essential to ensure food safety. In this study, a novel method based on cell elongation induced by beta-lactam antibiotics for direct microscopic counting of Gram-negative bacteria was established. Combined with the sample preparation steps of membrane filtration and magnetic separation, the detection of E. coli O157:H7 and Salmonella enterica serotype Typhimurium was achieved by direct optical microscopic counting of the number of elongated bacteria. The limit of detection of E. coli O157:H7 and S. typhimurium could reach 20 CFU mL^-1. The recovery tests for E. coli O157:H7 and S. typhimurium in water and milk samples showed acceptable recovery values between 93.6% and 106.2%. This method is sensitive, cost effective, and rapid (<2 h) and shows great potential for the detection of Gram-negative pathogens in various environmental and food samples.

Biomimetic human lung-on-a-chip for modeling disease investigation

The lung is the primary respiratory organ of the human body and has a complicated and precise tissue structure. It comprises conductive airways formed by the trachea, bronchi and bronchioles, and many alveoli, the smallest functional units where gas-exchange occurs via the unique gas-liquid exchange interface known as the respiratory membrane. In vitro bionic simulation of the lung or its microenvironment, therefore, presents a great challenge, which requires the joint efforts of anatomy, physics, material science, cell biology, tissue engineering, and other disciplines. With the development of micromachining and miniaturization technology, the concept of a microfluidics-based organ-on-a-chip has received great attention. An organ-on-a-chip is a small cell-culture device that can accurately simulate tissue and organ functions in vitro and has the potential to replace animal models in evaluations of drug toxicity and efficacy. A lung-on-a-chip, as one of the first proposed and developed organs-on-a-chip, provides new strategies for designing a bionic lung cell microenvironment and for in vitro construction of lung disease models, and it is expected to promote the development of basic research and translational medicine in drug evaluation, toxicological detection, and disease model-building for the lung. This review summarizes current lungs-on-a-chip models based on the lung-related cellular microenvironment, including the latest advances described in studies of lung injury, inflammation, lung cancer, and pulmonary fibrosis. This model should see effective use in clinical medicine to promote the development of precision medicine and individualized diagnosis and treatment.

Size-matching hierarchical micropillar arrays for detecting circulating tumor cells in breast cancer patients' whole blood

Circulating tumor cells (CTCs) are important markers for cancer diagnosis and treatment, but it is still a challenge to recognize and isolate CTCs because they are very rare in the blood. To selectively recognize CTCs and improve the capture efficiency, micro/nanostructured substrates have been fabricated for this application; however the size of CTCs is often ignored in designing and engineering micro/nanostructured substrates. Herein, a spiky polymer micropillar array is fabricated for capturing CTCs with high efficiency. The surface of the micropillar is cactus-like, and is composed of nanospikes. This hierarchical polymer array is designed according to the size of CTCs, which allows for more interactions of the CTCs with the array by setting the size of gaps among the micropillars to match with the CTCs. This polymer array is created by molding on an ordered silicon array, and then it is coated with an antiepithelial cell adhesion molecule antibody (anti-EpCAM). After co-culture with MCF-7 cells for 45 min, the capture efficiency of this array for CTCs is up to 91% ± 2%. Moreover, the anti-EpCAM modified polymer micropillar arrays present an excellent capacity to isolate CTCs from the whole blood samples of breast cancer patients. This study may provide a new concept for capturing target cells by designing and engineering micro/nanostructured substrates according to the size of target cells.

A micro-/nano-chip and quantum dots-based 3D cytosensor for quantitative analysis of circulating tumor cells

BACKGROUND

Due to the high transfer ability of cancer cell, cancer has been regarded as a world-wide high mortality disease. Quantitative analysis of circulating tumor cells (CTCs) can provide some valuable clinical information that is particularly critical for cancer diagnosis and treatment. Along with the rapid development of micro-/nano-fabrication technique, the three-dimensional (3D) bionic interface-based analysis method has become a hot research topic in the area of nanotechnology and life science. Micro-/nano-structure-based devices have been identified as being one of the easiest and most effective techniques for CTCs capture applications.

METHODS

We demonstrated an electrospun nanofibers-deposited nickel (Ni) micropillars-based cytosensor for electrochemical detection of CTCs. Breast cancer cell line with rich EpCAM expression (MCF7) were selected as model CTCs. The ultra-long poly (lactic-co-glycolic acid) (PLGA) nanofibers were firstly-crosswise stacked onto the surface of Ni micropillars by electrospinning to construct a 3D bionic interface for capturing EpCAM-expressing CTCs, following immuno-recognition with quantum dots functionalized anti-EpCAM antibody (QDs-Ab) and forming immunocomplexes on the micro-/nano-chip.

RESULTS

The Ni micropillars in the longitudinal direction not only play a certain electrical conductivity in the electrochemical detection, but also its special structure improves the efficiency of cell capture. The cross-aligned nanofibers could simulate the extracellular matrix to provide a good microenvironment which is better for cell adhesion and physiological functions. Bioprobe containing quantum dots will release Cd2+ in the process of acid dissolution, resulting in a change in current. Beneath favourable conditions, the suggested 3D cytosensor demonstrated high sensitivity with a broad range of 101-105 cells mL-1 and a detection limit of 8 cells mL-1.

CONCLUSIONS

We constructed a novel 3D electrochemical cytosensor based on Ni micropillars, PLGA electrospun nanofibers and quantum dots bioprobe, which could be used to highly sensitive and selective analysis of CTCs. More significantly, the 3D cytosensor can efficiently identify CTCs from whole blood, which suggested the potential applications of our technique for the clinical diagnosis and therapeutic monitoring of cancers.

Microfluidic Impedance Cytometer with Inertial Focusing and Liquid Electrodes for High-Throughput Cell Counting and Discrimination

In this paper, we present a novel impedance microcytometer integrated with inertial focusing and liquid electrode techniques for high-throughput cell counting and discrimination. The inertial prefocusing unit orders cells into a determinate train to reduce the possibility of cell adhesions and ensure that only one cell passes through detection region at a time, which improves the accuracy of downstream detection. The liquid electrodes are constructed by inserting Ag/AgCl wires into the electrode chambers filled with flowing highly conductive electrolyte solutions, which have a high detection sensitivity while requiring a simple fabrication process. The effects of main sample flow rate, feed flow rate in electrode chambers, and feed solution type on measured impedance signals are experimentally explored. On the basis of the optimized system, we establish a linear relationship between the amplitude of impedance peaks and the volume of size-calibrated particles and achieve a high detection throughput of ∼5000 cells/s. Finally, using the calibrated microcytometer, we further investigate the size distributions of human breast tumor cells (MCF-7 cells) and leukocytes (white blood cells (WBCs)) and set a threshold amplitude to successfully distinguish the MCF-7 cells spiked in WBCs. Our impedance microcytometer may provide a potential tool for label-free cell enumeration and identification.

Rapid and Sensitive Detection of Cancer Cells Based on the Photothermal Effect of Graphene Functionalized Magnetic Microbeads

A strategy based on an immune-graphene oxide (GO)-magnetic microbead complex for the sensitive, rapid, portable, and low-cost detection of cancer cells was developed. The high-efficiency cell capture and high sensitive thermal contrast detection could be simultaneously achieved using magnetic microbeads and the photothermal effect of GOs. The temperature variation caused by irradiating the GOs with a laser was used to establish the standard curve of temperature variation and cancer cell number. Under optimal conditions, the limit of detection could reach 100 cells. 4T1 cells spiked in human blood could be successfully detected in 1.5 h, and the recovery was between 90.8% and 116.5%.

Combination of Mechanical and Molecular Filtration for Enhanced Enrichment of Circulating Tumor Cells

Circulating tumor cells (CTCs) have been linked to cancer progression but are difficult to isolate, as they are very rare and heterogeneous, covering a range of sizes and expressing different molecular receptors. Filtration has emerged as a simple and powerful method to enrich CTCs but only captures cells above a certain size regardless of molecular characteristics. Here, we introduce antibody-functionalized microfilters to isolate CTCs based on both size and surface receptor expression. We present a 3D printed filtration cartridge with microfabricated polymer filters with 8, 10, 12, 15, or 20 μm-diameter pores. Pristine filters were used to optimize sample dilution, rinsing protocol, flow rate, and pore size, leading to >80% for the recovery of spiked cancer cells with very low white blood cell contamination (<1000). Then, filters were functionalized with antibodies against either epithelial cell adhesion molecule (EpCAM) or epidermal growth factor receptor (EGFR) and the cartridges were used to enrich breast (MDA-MB-231, MCF-7) and renal (786-O, A-498) cancer cells expressing various levels of EpCAM and EGFR. Cancer cells were spiked into human blood, and when using filters with antibodies specific to a molecular receptor expressed on a cell, efficiency was increased to >96%. These results suggest that filtration can be optimized to target specific CTC characteristics such as size and receptor expression and that a diverse range of CTCs may be captured using particular combinations of pore size, filtration parameters, and antibody functionalization.

In Vivo Capture of Circulating Tumor Cells Based on Transfusion with a Vein Indwelling Needle

Detection of circulating tumor cells (CTCs) could be used as a "liquid biopsy" for tracking the spread of cancer. In vitro detection methods based on blood sampling and in vitro CTC capture often suffer from the small sampling volume and sampling error. Here, the in vivo capture of CTCs based on transfusion with a surface-modified vein indwelling needle is proposed. When the needle was applied to transfusion in the vein, the simultaneous capture of CTCs was performed. To investigate the actual capture efficiency of the in vivo capture method, labeled MCF-7 cells were directly injected into the veins of rabbits, wild type mice, and nude mice and could be successfully captured. Two of 5 MCF-7 cells injected into the veins of nude mice were successfully captured. To investigate the CTC capture of mouse tumor model and compare with the in vitro method, mice were subcutaneous inoculated with metastatic 4T1 cells. Seven and 21 days after inoculation, CTCs were captured for the first time using in vivo and in vitro methods, respectively. This predicted that the in vivo method could be more suitable for use of early diagnosis of cancer than the in vitro method. As CTC capture can be performed at the same time as transfusion and does not cause further bodily harm, it would be easily accepted by patients. This efficient, simple, and less damaging method involving the use of a vein indwelling needle could be popularized easily in the clinic.