Improved SERS Nanoparticles for Direct Detection of Circulating Tumor Cells in the Blood

Immunological nanomaterials to combat cancer metastasis

Metastasis causes greater than 90% of cancer-associated deaths, presenting huge challenges for detection and efficient treatment of cancer due to its high heterogeneity and widespread dissemination to various organs. Therefore, it is imperative to combat cancer metastasis, which is the key to achieving complete cancer eradication. Immunotherapy as a systemic approach has shown promising potential to combat metastasis. However, current clinical immunotherapies are not effective for all patients or all types of cancer metastases owing to insufficient immune responses. In recent years, immunological nanomaterials with intrinsic immunogenicity or immunomodulatory agents with efficient loading have been shown to enhance immune responses to eliminate metastasis. In this review, we would like to summarize various types of immunological nanomaterials against metastasis. Moreover, this review will summarize a series of immunological nanomaterial-mediated immunotherapy strategies to combat metastasis, including immunogenic cell death, regulation of chemokines and cytokines, improving the immunosuppressive tumour microenvironment, activation of the STING pathway, enhancing cytotoxic natural killer cell activity, enhancing antigen presentation of dendritic cells, and enhancing chimeric antigen receptor T cell therapy. Furthermore, the synergistic anti-metastasis strategies based on the combinational use of immunotherapy and other therapeutic modalities will also be introduced. In addition, the nanomaterial-mediated imaging techniques (e.g., optical imaging, magnetic resonance imaging, computed tomography, photoacoustic imaging, surface-enhanced Raman scattering, radionuclide imaging, etc.) for detecting metastasis and monitoring anti-metastasis efficacy are also summarized. Finally, the current challenges and future prospects of immunological nanomaterial-based anti-metastasis are also elucidated with the intention to accelerate its clinical translation.

Optical nanomaterial-based detection of biomarkers in liquid biopsy

Liquid biopsy, which is a minimally invasive procedure as an alternative to tissue biopsy, has been introduced as a new diagnostic/prognostic measure. By screening disease-related markers from the blood or other biofluids, it promises early diagnosis, timely prognostication, and effective treatment of the diseases. However, there will be a long way until its realization due to its conceptual and practical challenges. The biomarkers detected by liquid biopsy, such as circulating tumor cell (CTC) and circulating tumor DNA (ctDNA), are extraordinarily rare and often obscured by an abundance of normal cellular components, necessitating ultra-sensitive and accurate detection methods for the advancement of liquid biopsy techniques. Optical biosensors based on nanomaterials open an important opportunity in liquid biopsy because of their enhanced sensing performance with simple and practical properties. In this review article, we summarized recent innovations in optical nanomaterials to demonstrate the sensitive detection of protein, peptide, ctDNA, miRNA, exosome, and CTCs. Each study prepares the optical nanomaterials with a tailored design to enhance the sensing performance and to meet the requirements of each biomarker. The unique optical characteristics of metallic nanoparticles (NPs), quantum dots, upconversion NPs, silica NPs, polymeric NPs, and carbon nanomaterials are exploited for sensitive detection mechanisms. These recent advances in liquid biopsy using optical nanomaterials give us an opportunity to overcome challenging issues and provide a resource for understanding the unknown characteristics of the biomarkers as well as the mechanism of the disease.

Nanomaterial-Based Strategies for Preventing Tumor Metastasis by Interrupting the Metastatic Biological Processes

Tumor metastasis is the primary cause of cancer-related deaths. The prevention of tumor metastasis has garnered notable interest and interrupting metastatic biological processes is considered a potential strategy for preventing tumor metastasis. The tumor microenvironment (TME), circulating tumor cells (CTCs), and premetastatic niche (PMN) play crucial roles in metastatic biological processes. These processes can be interrupted using nanomaterials due to their excellent physicochemical properties. However, most studies have focused on only one aspect of tumor metastasis. Here, the hypothesis that nanomaterials can be used to target metastatic biological processes and explore strategies to prevent tumor metastasis is highlighted. First, the metastatic biological processes and strategies involving nanomaterials acting on the TME, CTCs, and PMN to prevent tumor metastasis are briefly summarized. Further, the current challenges and prospects of nanomaterials in preventing tumor metastasis by interrupting metastatic biological processes are discussed. Nanomaterial-and multifunctional nanomaterial-based strategies for preventing tumor metastasis are advantageous for the long-term fight against tumor metastasis and their continued exploration will facilitate rapid progress in the prevention, diagnosis, and treatment of tumor metastasis. Novel perspectives are outlined for developing more effective strategies to prevent tumor metastasis, thereby improving the outcomes of patients with cancer.

Multiplexed Surface Protein Detection and Cancer Classification Using Gap-Enhanced Magnetic-Plasmonic Core-Shell Raman Nanotags and Machine Learning Algorithm

Cancer is the second leading cause of death attributed to disease worldwide. Current standard detection methods often rely on a single cancer marker, which can lead to inaccurate results, including false negatives, and an inability to detect multiple cancers simultaneously. Here, we developed a multiplex method that can effectively detect and classify surface proteins associated with three distinct types of breast cancer by utilizing gap-enhanced Raman scattering nanotags and machine learning algorithm. We synthesized anisotropic magnetic core-gold shell gap-enhanced Raman nanotags incorporating three different Raman reporters. These multicolor Raman nanotags were employed to distinguish specific surface protein markers in breast cancer cells. The acquired signals were deconvoluted and analyzed using classical least-squares regression to generate a surface protein profile and characterize the breast cancer cells. Furthermore, computational data obtained via finite-difference time-domain and discrete dipole approximation showed the amplification of the electric fields within the gap region due to plasmonic coupling between the two gold layers. Finally, a random forest classifier achieved an impressive classification and profiling accuracy of 93.9%, enabling effective distinguishing between the three different types of breast cancer cell lines in a mixed solution. With the combination of immunomagnetic multiplex target specificity and separation, gap-enhancement Raman nanotags, and machine learning, our method provides an accurate and integrated platform to profile and classify different cancer cells, giving implications for identification of the origin of circulating tumor cells in the blood system.

Application of microfluidic technology based on surface-enhanced Raman scattering in cancer biomarker detection: A review

With the continuous discovery and research of predictive cancer-related biomarkers, liquid biopsy shows great potential in cancer diagnosis. Surface-enhanced Raman scattering (SERS) and microfluidic technology have received much attention among the various cancer biomarker detection methods. The former has ultrahigh detection sensitivity and can provide a unique fingerprint. In contrast, the latter has the characteristics of miniaturization and integration, which can realize accurate control of the detection samples and high-throughput detection through design. Both have the potential for point-of-care testing (POCT), and their combination (lab-on-a-chip SERS (LoC-SERS)) shows good compatibility. In this paper, the basic situation of circulating proteins, circulating tumor cells, exosomes, circulating tumor DNA (ctDNA), and microRNA (miRNA) in the diagnosis of various cancers is reviewed, and the detection research of these biomarkers by the LoC-SERS platform in recent years is described in detail. At the same time, the challenges and future development of the platform are discussed at the end of the review. Summarizing the current technology is expected to provide a reference for scholars engaged in related work and interested in this field.

Ag decoration on Na2Ti3O7 nanowires for improved SERS and PHE performance

Na2Ti3O7 (NTO) is recognized as an authenticated promising photocatalyst and surface-enhanced Raman scattering (SERS) active material, although its performance is limited by its high carrier recombination rate, wide band gap and inadequate utilization of visible light. In this study, to solve these issues, sea urchin-shaped NTO nanowires directly grown on a substrate were fabricated, and then Ag nanoparticles were decorated on NTO nanowires using sputtering equipment. The as-prepared Ag-NTO substrates exhibited different morphologies and high SERS activity, which was confirmed by finite-difference time-domain (FDTD) simulations, showing that appropriate Ag decoration can bring more nanogaps and thus enhance the electromagnetic field (EM) contribution. We visualized the charge transfer (CT) mechanism in SERS and further investigated the catalytic hydrogen production process similarly induced by photogenerated CT. The optimal SERS substrate (Ag-NTO-3) was adopted to verify the photocatalytic hydrogen evolution (PHE) activity, and the hydrogen evolution rate of Ag-NTO-3 was 106.7 μmol h-1 (twice that of pristine NTO). Photoelectrochemical measurements and photoluminescence (PL) analysis were used to elucidate the potential enhancement mechanisms for the photocatalytic performance and CT process. This study can provide a valuable reference for performance and mechanism studies of SERS substrates and photocatalysts.

A novel dual-function SERS-based identification strategy for preliminary screening and accurate diagnosis of circulating tumor cells

Non-specific adsorption of bioprobes based on surface-enhanced Raman spectroscopy (SERS) technology inevitably endows white blood cells (WBC) in the peripheral blood with Raman signals, which greatly interfere the identification accuracy of circulating tumor cells (CTCs). In this study, an innovative strategy was proposed to effectively identify CTCs by using SERS technology assisted by a receiver operating characteristic (ROC) curve. Firstly, a magnetic Fe3O4-Au complex SERS bioprobe was developed, which could effectively capture the triple negative breast cancer (TNBC) cells and endow the tumor cells with distinct SERS signals. Then, the ROC curve obtained based on the comparison of SERS intensity of TNBC cells and WBC was used to construct a tumor cell identification model. The merit of the model was that the detection sensitivity and specificity could be intelligently switched according to different identification purposes such as accurate diagnosis or preliminary screening of tumor cells. Finally, the difunctional recognition ability of the model for accurate diagnosis and preliminary screening of tumor cells was further validated by using the healthy human blood added with TNBC cells and blood samples of real tumor patients. This novel difunctional identification strategy provides a new perspective for identification of CTCs based on the SERS technology.

Stimuli-Responsive Codelivery System Self-Assembled from in Situ Dynamic Covalent Reaction of Macrocyclic Disulfides for Cancer Magnetic Resonance Imaging and Chemotherapy

Supramolecular self-assembly has gained increasing attention to construct multicomponent drug delivery systems for cancer diagnosis and therapy. Despite that these self-assembled nanosystems present surprising properties beyond that of each subcomponent, the spontaneous nature of co-self-assembly causes significant difficulties in control of the synthesis process and consequently leads to unsatisfactory influences in downstream applications. Hence, we utlized an in situ dynamic covalent reaction based on thiol-disulfide exchange to slowly produce disulfide macrocycles, which subsequently triggered the co-self-assembly of an anticancer drug (doxorubicin, DOX) and a magnetic resonance imaging (MRI) contrast agent of ultrasmall iron oxide nanoparticles (IO NPs). It showed concentration regulation of macrocyclic disulfides, DOX, and IO NPs by a dynamic covalent self-assembly (DCS) strategy, resulting in a stable codelivery nanosystem with high drug loading efficiency of 37.36%. More importantly, disulfide macrocycles in the codelivery system could be reduced and broken by glutathione (GSH) in tumor cells, thus leading to disassembly of nanostructures and intellgent release of drugs. These stimuli-responsive performances have been investigated via morphologies and molecular structures, revealing greatly enhanced dual-modal MRI abilities and smart drug release under the trigger of GSH. Moreover, the codelivery system conjugated with a targeting molecule of cyclic Arg-Gly-Asp (cRGD) exhibited significant biocompatibility, MR imaging, and chemotherapeutic anticancer effect in vitro and in vivo. These results indicated that in situ dynamic covalent chemistry enhanced the control over co-self-assembly and paved the way to develop more potential drug delivery systems.

Gold nanorods with iron oxide dual-modal bioprobes in SERS-MRI enable accurate programmed cell death ligand-1 expression detection in triple-negative breast cancer

The efficiency of immunotherapy for triple-negative breast cancer (TNBC) is relatively low due to the difficulty in accurately detecting immune checkpoints. The detection of TNBC-related programmed cell death ligand-1 (PD-L1) expression is important to guide immunotherapy and improve treatment efficiency. Surface-enhanced Raman spectroscopy (SERS) and magnetic resonance (MR) imaging exhibit great potential for early TNBC diagnosis. SERS, an optical imaging mode, has the advantages of high detection sensitivity, good spatial resolution, and "fingerprint" spectral characteristics; however, the shallow detection penetration of SERS bioprobes limits its application in vivo. MR has the advantages of allowing deep penetration with no radiation; however, its spatial resolution needs to be improved. SERS and MR have complementary imaging features for tumor marker detection. In this study, gold nanorod and ultrasmall iron oxide nanoparticle composites were developed as dual-modal bioprobes for SERS-MRI to detect PD-L1 expression. Anti-PD-L1 (aPD-L1) was utilized to improve the targeting ability and specificity of PD-L1 expression detection. TNBC cells expressing PD-L1 were accurately detected via the SERS imaging mode in vitro, which can image at the single-cell level. In addition, bioprobe accumulation in PD-L1 expression-related tumor-bearing mice was simply and dynamically monitored and analyzed in vivo using MR and SERS. To the best of our knowledge, this is the first time a SERS-MRI dual-modal bioprobe combined with a PD-L1 antibody has been successfully used to detect PD-L1 expression in TNBC. This work paves the way for the design of high-performance bioprobe-based contrast agents for the clinical immunotherapy of TNBC.

Application of Metal-Based Nanomaterials in In Vitro Diagnosis of Tumor Markers: Summary and Prospect

Cancer, which presents with high incidence and mortality rates, has become a significant health threat worldwide. However, there is currently no effective solution for rapid screening and high-quality treatment of early-stage cancer patients. Metal-based nanoparticles (MNPs), as a new type of compound with stable properties, convenient synthesis, high efficiency, and few adverse reactions, have become highly competitive tools for early cancer diagnosis. Nevertheless, challenges such as the difference between the microenvironment of detected markers and the real-life body fluids remain in achieving widespread clinical application of MNPs. This review provides a comprehensive review of the research progress made in the field of in vitro cancer diagnosis using metal-based nanoparticles. By delving into the characteristics and advantages of these materials, this paper aims to inspire and guide researchers towards fully exploiting the potential of metal-based nanoparticles in the early diagnosis and treatment of cancer.

Using host-guest interactions at the interface of quantum dots to load drug molecules for biocompatible, safe, and effective chemo-photodynamic therapy against cancer

Combining photodynamic therapy (PDT) and chemotherapy (CHT) by loading an anti-cancer drug and a photosensitizer (PS) into the same delivery nanosystem has been proposed as an effective approach to achieve synergistic effects for a safe cancer treatment. However, exploring an ideal delivery nanosystem has been challenging, because the noncovalent interactions must be maintained between the multiple components to produce a stable yet responsive nanostructure that takes into account the encapsulation of drug molecules. We addressed this issue by engineering the interfacial interaction between Ag₂S quantum dots (QDs) using a pillararene derivative to direct the co-self-assembly of the entire system. The high surface area-to-volume ratio of the Ag₂S QDs provided ample hydrophobic space to accommodate the anti-drug molecule doxrubicine. Moreover, Ag₂S QDs served as PSs triggered by 808 nm near-infrared (NIR) light and also as carriers for high-efficiency delivery of drug molecules to the tumor site. Drug release experiments showed smart drug release under the acidic microenvironments (pH 5.5) in tumor cells. Additionally, the Ag₂S QDs demonstrated outstanding PDT ability under NIR light, as confirmed by extracellular and intracellular reactive oxygen species generation. Significant treatment efficacy of the chemo-photodynamic synergistic therapy for cancer using the co-delivery system was demonstrated via in vitro and in vivo studies. These findings suggest that our system offers intelligent control of CHT and PDT, which will provide a promising strategy for constructing hybrid systems with synergistic effects for advanced applications in biomedicine, catalysis, and optoelectronics.

Typing of cancer cells by microswimmer based on Co-Fe-MOF for one-step simultaneously detect multiple biomarkers

Capturing, identifying, and counting CTCs cancer cells that have escaped from the tumor and wandered into the bloodstream is a major challenge. We proposed a noval microswimmer dual-mode aptamer (electrochemical and fluorescent)-(Mapt-EF) homogeneous sensor with active capture/controlled release double signaling molecule/separation and release cell based on the Co-Fe-MOF nanomaterial for simultaneous one-step detection of multiple biomarkers protein tyrosine kinase-7 (PTK7), Epithelial cell adhesion molecule (EpCAM), and mucin-1 (MUC1) for diagnosis of multiple cancer cell types. The Co-Fe-MOF is a nano-enzyme capable of catalyzing the decomposition of hydrogen peroxide to release bubbles of oxygen, producing a driving force to conduct hydrogen peroxide through the liquid, and has the capacity to self-decompose during the catalytic process. Phosphoric acid is present in the aptamer chains of PTK7, EpCAM, and MUC1, and the aptamer chains are adsorbed to the surface of the Mapt-EF homogeneous sensor in the form of a gated switch to inhibit the catalytic decomposition activity of hydrogen peroxide. The Mapt-EF homogeneous sensor has the capability to actively target biomarkers that can be entrained by oxygen bubbles without being degraded. The detection time of the sensor was 20 min, the detection limits were 9.6 fg/mL, 8.4 fg/mL and 7.7 fg/mL with the linear range was 0-20 pg/mL, respectively. The Mapt-EF homogeneous sensor has high detection sensitivity, and its detection limit can reach the level of single cell at the lowest. The Mapt-EF homogeneous sensor has great application potential in clinical detection and analysis of tumor cells.

Electroporation-Assisted Surface-Enhanced Raman Detection for Long-Term, Label-Free, and Noninvasive Molecular Profiling of Live Single Cells

Molecule characterization of live single cells is greatly important in disease diagnoses and personalized treatments. Conventional molecule detection methods, such as mass spectrography, gene sequencing, or immunofluorescence, are usually destructive or labeled and unable to monitor the dynamic change of live cellular molecules. Herein, we propose an electroporation-assisted surface-enhanced Raman scattering (EP-SERS) method using a microchip to implement label-free, noninvasive, and continuous detections of the molecules of live single cells. The microchip containing microelectrodes with nanostructured EP-SERS probes has a multifunction of cell positioning, electroporation, and SERS detection. The EP-SERS method capably detects both the intracellular and extracellular molecules of live single cells without losing cell viability so as to enable long-term monitoring of the molecular pathological process in situ. We detect the molecules of single cells for two breast cancer cell lines with different malignancies (MCF-7 and MDA-MB-231), one liver cancer cell line (Huh-7), and one normal cell line (293T) using the EP-SERS method and classify these cell types to achieve high accuracies of 91.4-98.3% using their SERS spectra. Furthermore, 24 h continuous monitoring of the heterogeneous molecular responses of different cancer cell lines under doxorubicin treatment is successfully implemented using the EP-SERS method. This work provides a long-term, label-free, and biocompatible approach to simultaneously detect intracellular and extracellular molecules of live single cells on a chip, which would facilitate research and applications of cancer diagnoses and personalized treatments.

Manipulation and elimination of circulating tumor cells using multi-responsive nanosheet for malignant tumor therapy

Tumor recurrence caused by metastasis is a major cause of death for patients. Thus, a strategy to manipulate the circulating tumor cells (CTCs, initiators of tumor metastasis ) and eliminate them along with the primary tumor has significant clinical significance for malignant tumor therapy. In this study, a magnet-NIR-pH multi-responsive nanosheet (Fe₃O₄@SiO₂-GO-PEG-FA/AMP-DOX, FGPFAD) was fabricated to capture CTCs in circulation, then magnetically transport them to the primary tumor, and finally perform NIR-dependent photothermal therapy as well as acidic-environment-triggered chemotherapy to destroy both the CTCs and the primary tumor. The FGPFAD nanosheet consists of silica-coated ferroferric oxide nanoparticles (Fe₃O₄@SiO₂, magnetic targeting agent), graphene oxide (GO, photothermal therapy agent), polyethylene glycol (PEG, antifouling agent for sustained circulation), folic acid (FA, capturer of CTCs) and antimicrobial-peptide-conjugated doxorubicin (AMP-DOX, agent for chemotherapy), in which the AMP-DOX was bound to the FGPFAD nanosheet via a cleavable Schiff base to achieve acidic-environment-triggered drug release for tumor-specific chemotherapy. Both in vitro and in vivo results indicated that the effective capture and magnetically guided transfer of CTCs to the primary tumor, as well as the multimodal tumor extermination performed by our FGPFAD nanosheet, significantly inhibited the primary tumor and its metastasis.

Machine learning-augmented surface-enhanced spectroscopy toward next-generation molecular diagnostics

The world today is witnessing the significant role and huge demand for molecular detection and screening in healthcare and medical diagnosis, especially during the outbreak of COVID-19. Surface-enhanced spectroscopy techniques, including Surface-Enhanced Raman Scattering (SERS) and Infrared Absorption (SEIRA), provide lattice and molecular vibrational fingerprint information which is directly linked to the molecular constituents, chemical bonds, and configuration. These properties make them an unambiguous, nondestructive, and label-free toolkit for molecular diagnostics and screening. However, new issues in molecular diagnostics, such as increasing molecular species, faster spread of viruses, and higher requirements for detection accuracy and sensitivity, have brought great challenges to detection technology. Advancements in artificial intelligence and machine learning (ML) techniques show promising potential in empowering SERS and SEIRA with rapid analysis and automatic data processing to jointly tackle the challenge. This review introduces the combination of ML and SERS/SEIRA by investigating how ML algorithms can be beneficial to SERS/SEIRA, discussing the general process of combining ML and SEIRA/SERS, highlighting the molecular diagnostics and screening applications based on ML-combined SEIRA/SERS, and providing perspectives on the future development of ML-integrated SEIRA/SERS. In general, this review offers comprehensive knowledge about the recent advances and the future outlook regarding ML-integrated SEIRA/SERS for molecular diagnostics and screening.

Isolation, Detection and Analysis of Circulating Tumour Cells: A Nanotechnological Bioscope

Cancer is one of the dreaded diseases to which a sizeable proportion of the population succumbs every year. Despite the tremendous growth of the health sector, spanning diagnostics to treatment, early diagnosis is still in its infancy. In this regard, circulating tumour cells (CTCs) have of late grabbed the attention of researchers in the detection of metastasis and there has been a huge surge in the surrounding research activities. Acting as a biomarker, CTCs prove beneficial in a variety of aspects. Nanomaterial-based strategies have been devised to have a tremendous impact on the early and rapid examination of tumor cells. This review provides a panoramic overview of the different nanotechnological methodologies employed along with the pharmaceutical purview of cancer. Initiating from fundamentals, the recent nanotechnological developments toward the detection, isolation, and analysis of CTCs are comprehensively delineated. The review also includes state-of-the-art implementations of nanotechnological advances in the enumeration of CTCs, along with future challenges and recommendations thereof.

Fluorescence anisotropy cytosensing of folate receptor positive tumor cells using 3D polyurethane-GO-foams modified with folic acid: molecular dynamics and in vitro studies

Integrated polyurethane (PU)-based foams modified with PEGylated graphene oxide and folic acid (PU@GO-PEG-FA) were developed with the goal of capturing and detecting tumor cells with precision. The detection of the modified PU@GO-PEG surface through FA against folate receptor-overexpressed tumor cells is the basis for tumor cell capture. Molecular dynamics (MD) simulations were applied to study the strength of FA interactions with the folate receptor. Based on the obtained results, the folate receptor has intense interactions with FA, which leads to the reduction in the FA interactions with PEG, and so decreases the fluorescence intensity of the biosensor. The synergistic interactions offer the FA-modified foams a high efficiency for capturing the tumor cell. Using a turn-off fluorescence technique based on the complicated interaction of FA-folate receptor generated by target recognition, the enhanced capture tumor cells could be directly read out at excitation-emission wavelengths of 380-450 nm. The working range is between 1×10 ² to 2×10 ⁴ cells mL ^-1 with a detection limit of 25 cells mL ^-1 and good reproducibility with relative standard deviation of 2.35%. Overall, findings demonstrate that the fluorescence-based biosensor has a significant advantage for early tumor cell diagnosis.

Nanomaterials meet surface-enhanced Raman scattering towards enhanced clinical diagnosis: a review

Surface-enhanced Raman scattering (SERS) is a very promising tool for the direct detection of biomarkers for the diagnosis of i.e., cancer and pathogens. Yet, current SERS strategies are hampered by non-specific interactions with co-existing substances in the biological matrices and the difficulties of obtaining molecular fingerprint information from the complex vibrational spectrum. Raman signal enhancement is necessary, along with convenient surface modification and machine-based learning to address the former issues. This review aims to describe recent advances and prospects in SERS-based approaches for cancer and pathogens diagnosis. First, direct SERS strategies for key biomarker sensing, including the use of substrates such as plasmonic, semiconductor structures, and 3D order nanostructures for signal enhancement will be discussed. Secondly, we will illustrate recent advances for indirect diagnosis using active nanomaterials, Raman reporters, and specific capture elements as SERS tags. Thirdly, critical challenges for translating the potential of the SERS sensing techniques into clinical applications via machine learning and portable instrumentation will be described. The unique nature and integrated sensing capabilities of SERS provide great promise for early cancer diagnosis or fast pathogens detection, reducing sanitary costs but most importantly allowing disease prevention and decreasing mortality rates.

Double spiral chip-embedded micro-trapezoid filters (SMT filters) for the sensitive isolation of CTCs of prostate cancer by spectral detection

Circulating tumor cells (CTCs) are cancer cells that are released from the original tumor and circulate in the blood vessels, carrying greatly similar constituents as the original tumor. Therefore, CTCs have a significant value in cancer prognosis, early diagnosis, and anti-cancer therapy. However, their rarity and heterogeneity make the isolation of CTCs an arduous task. In the present research, we propose a double spiral chip-embedded micro-trapezoid filter (SMT filter) for the sensitive isolation of the CTCs of prostate cancer by spectral detection. SMT filters were elongated to effectively capture CTCs and this distinctive design was conducive to their isolation and enrichment. The SMT filters were verified with tumor cells and artificial patient blood with a capture efficiency as high as 94% at a flow rate of 1.5 mL h^-1. As a further validation, the SMT filters were validated in isolating CTCs from 10 prostate cancers and other cancers in 4 mL blood samples. Also, the CTCs tested positive for each patient blood sample, ranging from 83-114 CTCs. Significantly, we advanced hyperspectral imaging to detect the characteristic spectrum of CTCs both captured in situ on SMT filters and enriched after isolation. The CTCs could be positively identified by hyperspectral imaging with complete integrity of the cell morphology and an improved characteristic spectrum. This represents a breakthrough in the conventional surface-enhanced Raman scattering (SERS) spectroscopy of nanoparticles. Also, the characteristic spectrum of the CTCs would be highly beneficial for distinguishing the cancer type and accurate for enumerating tumor cells with varied intensities. Furthermore, a novel integrated flower-shaped microfilter was presented with all these aforementioned merits. The success of both the SMT filters and characteristic spectral detection indicated their feasibility for further clinical analysis, the evaluation of cancer therapy, and for potential application.

Recent advances in the potential applications of luminescence-based, SPR-based, and carbon-based biosensors

Abstract

The need for biosensors has evolved in the detection of molecules, diseases, and pollution from various sources. This requirement has headed to the development of accurate and powerful equipment for analysis using biological sensing component as a biosensor. Biosensors have the advantage of rapid detection that can beat the conventional methods for the detection of the same molecules. Bio-chemiluminescence-based sensors are very sensitive during use in biological immune assay systems. Optical biosensors are emerging with time as they have the advantage that they act with a change in the refractive index. Carbon nanotube-based sensors are another area that has an important role in the biosensor field. Bioluminescence gives much higher quantum yields than classical chemiluminescence. Electro-generated bioluminescence has the advantage of miniature size and can produce a high signal-to-noise ratio and the controlled emission. Recent advances in biological techniques and instrumentation involving fluorescence tag to nanomaterials have increased the sensitivity limit of biosensors. Integrated approaches provided a better perspective for developing specific and sensitive biosensors with high regenerative potentials. This paper mainly focuses on sensors that are important for the detection of multiple molecules related to clinical and environmental applications.

Key points

• The review focusses on the applications of luminescence-based, surface plasmon resonance-based, carbon nanotube-based, and graphene-based biosensors

• Potential clinical, environmental, agricultural, and food industry applications/uses of biosensors have been critically reviewed

• The current limitations in this field are discussed, as well as the prospects for future advancement

Circulating tumor DNA in cancer diagnosis, monitoring, and prognosis

BACKGROUND

Circulating tumor DNA (ctDNA) has become one of the crucial components for cancer detection with the increase of precision medicine practice. ctDNA has great potential as a blood-based biomarker for the detection and treatment of cancer in its early stages. The purpose of this article was to discuss ctDNA and how it can be utilized to detect cancer. The benefits and drawbacks of this cancer detection technology, as well as the field's future possibilities in various cancer management scenarios, are discussed. MAIN TEXT: ctDNA has clinical applications in disease diagnosis and monitoring. It can be used to identify mutations of interest and genetic heterogeneity. Another use of ctDNA is to monitor the effects of therapy by detecting mutation-driven resistance. Different technologies are being used for the detection of ctDNA. Next-generation sequencing, digital PCR, real-time PCR, and mass spectrometry are used. Using dPCR makes it possible to partition and analyze individual target sequences from a complex mixture. Mass-spectrometry technology enables accurate detection and quantification of ctDNA mutations at low frequency. Surface-enhanced Raman spectroscopy (SERS) and UltraSEEK are two systems based on this technology. There is no unified standard for detecting ctDNA as it exists in a low concentration in blood. As there is no defined approach, false positives occur in several methods due to inadequate sensitivities. Techniques used in ctDNA are costly and there is a limitation in clinical settings.

SHORT CONCLUSION

A detailed investigation is urgently needed to increase the test's accuracy and sensitivity. To find a standard marker for all forms of cancer DNA, more study is needed. Low concentrations of ctDNA in a sample require improved technology to provide the precision that low concentrations of ctDNA in a sample afford.

TiO2-Based Bioprobe Enabling Excellent SERS Activity in Detection of Diverse Circulating Tumor Cells

Circulating tumor cells (CTCs), can be the seeds of tumor metastasis, and are closely linked to cancer-related death. Fast and effective detection of CTCs is important for early diagnosis of...

State-of-the-arts techniques and current evolving approaches in the separation and detection of circulating tumor cell

Circulating tumor cells (CTCs) are cancer cells that shed from the primary tumor and then enter the circulatory system, a small part of which may evolve into metastatic cancer under appropriate microenvironment conditions. The detection of CTCs is a truly noninvasive, dynamic monitor for disease changes, which has considerable clinical implications in the selection of targeted drugs. However, their inherent rarity and heterogeneity pose significant challenges to their isolation and detection. Even the "gold standard", CellSearch™, suffers from high expenses, low capture efficiency, and the consumption of time. With the advancement of CTCs analysis technologies in recent years, the yield and efficiency of CTCs enrichment have gradually been improved, as well as detection sensitivity. In this review, the isolation and detection strategies of CTCs have been completely described and the potential directions for future research and development have also been highlighted through analyzing the challenges faced by current strategies.

Nanostructure-based surface-enhanced Raman scattering for diagnosis of cancer

Cancer is a malignant disease that seriously affects human health and life. Early diagnosis and timely treatment can significantly improve the survival rate of cancer patients. Surface-enhanced Raman scattering (SERS) is an optical technology that can detect and image samples at the single-molecule level. It has the advantages of rapidity, high specificity, high sensitivity and no damage to the sample. The performance of SERS is highly dependent on the properties, size and morphology of the SERS substrate. Preparation of SERS substrates with good reproducibility and chemical stability is a key factor in realizing the wide application of SERS technology in cancer diagnosis. In this review we provide a detailed presentation of the latest research on SERS in cancer diagnosis and the detection of cancer biomarkers, mainly focusing on nanotechnological approaches in cancer diagnosis by using SERS. We also consider the future development of nanostructure-based SERS in cancer diagnosis.

Recent Development of Nanomaterials-Based Cytosensors for the Detection of Circulating Tumor Cells

The accurate analysis of circulating tumor cells (CTCs) holds great promise in early diagnosis and prognosis of cancers. However, the extremely low abundance of CTCs in peripheral blood samples limits the practical utility of the traditional methods for CTCs detection. Thus, novel and powerful strategies have been proposed for sensitive detection of CTCs. In particular, nanomaterials with exceptional physical and chemical properties have been used to fabricate cytosensors for amplifying the signal and enhancing the sensitivity. In this review, we summarize the recent development of nanomaterials-based optical and electrochemical analytical techniques for CTCs detection, including fluorescence, colorimetry, surface-enhanced Raman scattering, chemiluminescence, electrochemistry, electrochemiluminescence, photoelectrochemistry and so on.

In Situ Single Cell Proteomics Reveals Circulating Tumor Cell Heterogeneity during Treatment

Cancer is a dynamic disease with heterogenic molecular signatures and constantly evolves during the course of the disease. Single cell proteomic analysis could offer a suitable pathway to monitor cancer cell heterogeneity and deliver critical information for the diagnosis, recurrence, and drug-resistant mechanisms in cancer. Current standard techniques for proteomic analysis such as ELISA, mass spectrometry, and Western blots are time-consuming, expensive, and often require fluorescence labeling that fails to provide accurate information about the multiple protein expression changes at the single cell level. Herein, we report a surface-enhanced Raman spectroscopy-based simple microfluidic device that enables the screening of single circulating tumor cells (CTC) in a dynamic state to precisely understand the heterogeneous expression of multiple protein biomarkers in response to therapy. It further enables identifying intercellular heterogeneous expression of CTC surface proteins which would be highly informative to identify the cancer cells surviving treatment and potentially responsible for drug resistance. Using a bead and cell line-based model system, we successfully detect single bead and single cell spectra when flowed through the device. Using SK-MEL-28 melanoma cells, we demonstrate that our system is capable of monitoring heterogeneous expressions of multiple surface protein markers (MCSP, MCAM, and LNGFR) before and during drug treatment. Integrating a label-free electrochemical system with the device, we also monitor the expression of an intracellular protein (here, BRAF^V600E) under drug treatment. Finally, we perform a longitudinal study with 15 samples from five different melanoma patients who underwent therapy. We find that the average expression of receptor proteins in a patient fails to determine the therapy response particularly when the disease progresses. However, single CTC analysis with our device shows a high level of intercellular heterogeneity in the receptor expression profiles of patient-derived CTCs and identifies heterogeneity within CTCs. More importantly, we find that a fraction of CTCs still shows a high expression of these receptor proteins during and after therapy, indicating the presence of resistant CTCs which may evolve after a certain time and progress the disease. We believe this automated assay will have high clinical importance in disease diagnosis and monitoring treatment and will significantly advance the understanding of cancer heterogeneity on the single cell level.

Emerging Applications of Nanotechnology in Healthcare Systems: Grand Challenges and Perspectives

Healthcare, as a basic human right, has often become the focus of the development of innovative technologies. Technological progress has significantly contributed to the provision of high-quality, on-time, acceptable, and affordable healthcare. Advancements in nanoscience have led to the emergence of a new generation of nanostructures. Each of them has a unique set of properties that account for their astonishing applications. Since its inception, nanotechnology has continuously affected healthcare and has exerted a tremendous influence on its transformation, contributing to better outcomes. In the last two decades, the world has seen nanotechnology taking steps towards its omnipresence and the process has been accelerated by extensive research in various healthcare sectors. The inclusion of nanotechnology and its allied nanocarriers/nanosystems in medicine is known as nanomedicine, a field that has brought about numerous benefits in disease prevention, diagnosis, and treatment. Various nanosystems have been found to be better candidates for theranostic purposes, in contrast to conventional ones. This review paper will shed light on medically significant nanosystems, as well as their applications and limitations in areas such as gene therapy, targeted drug delivery, and in the treatment of cancer and various genetic diseases. Although nanotechnology holds immense potential, it is yet to be exploited. More efforts need to be directed to overcome these limitations and make full use of its potential in order to revolutionize the healthcare sector in near future.

A PLGA nanofiber microfluidic device for highly efficient isolation and release of different phenotypic circulating tumor cells based on dual aptamers

The isolation of specific and sensitive circulating tumor cells (CTCs) is significant for applying them in cancer diagnosis and monitoring. In this work, dual aptamer-modified poly(lactic-co-glycolic acid) (PLGA) nanofiber-based microfluidic devices were fabricated to achieve the highly efficient capture and specific release of epithelial and mesenchymal CTCs of ovarian cancer. Dual aptamer targeting epithelial cell adhesion molecules (EpCAM) and N-cadherin proteins to improve the capture sensitivity, bovine serum albumin (BSA) to guarantee the capture purity and the nanofibers to increase the capture efficiency via synchronously and effectively capturing the epithelial and mesenchymal CTCs with good capture specificity and sensitivity from blood samples were used. We used the target cells including the ovarian cancer A2780 cells (N-cadherin-high, EpCAM-low) and OVCAR-3 cells (EpCAM-high, N-cadherin-low) to test the devices, which exhibited good capture efficiency (91% for A2780 cells, 89% for OVCAR-3 cells), release efficiency (95% for A2780 cells, 88% for OVCAR-3 cells), and sensitivity for rare cells (92% for A2780 cells, 88% for OVCAR-3 cells). Finally, the clinical blood samples of ovarian cancer patients were detected by the PLGA nanofiber-based microfluidic device, and 1 to 13 CTCs were successfully confirmed to be captured with the help of immunofluorescence staining identification. The results exhibited that the dual aptamer-modified PLGA nanofiber-based microfluidic device used as a tool for CTC capture has the potential for clinical application to guide the diagnosis, treatment, and prognosis of ovarian cancer patients.

Octahedral silver oxide nanoparticles enabling remarkable SERS activity for detecting circulating tumor cells

The detection of circulating tumor cells (CTCs) is a crucial tool for early cancer diagnosis, prognosis, and postoperative evaluation. However, detection sensitivity remains a major challenge because CTCs are extremely rare in peripheral blood. To effectively detect CTCs, octahedral Ag₂O nanoparticles (NPs) with high dispersibility, good biocompatibility, remarkable surface-enhanced Raman scattering (SERS) enhancement, and obvious enhancement selectivity are designed as an SERS platform. Ag₂O NPs with many oxygen vacancy defects are successfully synthesized, which exhibit an ultra-high SERS enhancement factor (1.98×10⁶) for 4-mercaptopyridine molecules. The remarkable SERS activity of octahedral Ag₂O NPs is derived from the synergistic effect of the surface defect-promoted photo-induced charge transfer (PICT) process and strong vibration coupling resonance in the Ag₂O-molecule SERS complex, greatly amplifying the molecular Raman scattering cross-section. The promoted PICT process is confirmed using ultraviolet-visible (UV-Vis) absorption spectroscopy, demonstrating that obvious PICT resonance occurs in Ag₂O SERS system under visible light. An additional growth step of SERS bioprobe is proposed by modifying the Raman signal molecules and functional biological molecules on Ag₂O NPs for CTC detection. The Ag₂O-based SERS bioprobe exhibits excellent detection specificity for different cancer cells in rabbit blood. Importantly, the high-sensitivity Ag₂O-based SERS bioprobe satisfies the requirement for rare CTC detection in the peripheral blood of cancer patients, and the detection limit can reach 1 cell per mL. To our knowledge, this study is the first time that a semiconductor SERS substrate has been successfully utilized in CTC detection. This work provides new insights into CTC detection and the development of novel semiconductor-based SERS platforms for cancer diagnosis.

Boosting the sub-cellular biomolecular cancer signals by self-functionalized tag-free nano sensor

Surface Enhanced Raman Scattering (SERS)-based sub-cellular cancer diagnosis can simultaneously obtain multiple biomolecular signals crucial in diagnostic platform for a heterogeneous disease like cancer. But, SERS-probes being typically tagged with chemical functionalization demonstrate limitations due to adverse biocompatibility, ineffective cellular internalization, SERS-signal quenching and spectral contamination. Although, tag-free SERS-probes overcome these limitations; complexity in spectral interpretation and detection insensitivity make it disadvantageous. In this study, we have exploited the inherent charges of cellular biomolecules and introduced self-functionalized complementary charged, tag-free SERS nano probes for biomolecule-specific investigation. Extremely small nano probes (sub 10 nm), synthesized with multiphoton ionization were functionalized with charge by physical synthesis without any ligands or chemical processes. The probes demonstrated significant SERS (EF~10⁶) with analyte molecules (4ATP & 4MBA). Multifold signal boost was achieved for the signals of cellular components - amplification of ~7 fold for DNA, ~16 fold for proteins and ~24 fold for lipids with the commentary charged nano probes as compared to the neutral nano probes. The signal boost was attributed to the efficient delivery of extremely small, complementary charged probes to the cellular biomolecules of interest enabling simultaneous detection of sub-cellular biomolecules such as DNA, proteins and lipids and with high reproducibility. Cancer classification and investigation of drug resistance in cancer with single cell sensitivity was demonstrated. Such biomolecule-specific investigation of cancer from intact cells will open pathways for comprehensive cancer diagnosis.

Immunoengineered magnetic-quantum dot nanobead system for the isolation and detection of circulating tumor cells

Background

Highly efficient capture and detection of circulating tumor cells (CTCs) remain elusive mainly because of their extremely low concentration in patients’ peripheral blood.

Methods

We present an approach for the simultaneous capturing, isolation, and detection of CTCs using an immuno-fluorescent magnetic nanobead system (iFMNS) coated with a monoclonal anti-EpCAM antibody.

Results

The developed antibody nanobead system allows magnetic isolation and fluorescent-based quantification of CTCs. The expression of EpCAM on the surface of captured CTCs could be directly visualized without additional immune-fluorescent labeling. Our approach is shown to result in a 70–95% capture efficiency of CTCs, and 95% of the captured cells remain viable. Using our approach, the isolated cells could be directly used for culture, reverse transcription-polymerase chain reaction (RT-PCR), and immunocytochemistry (ICC) identification. We applied iFMNS for testing CTCs in peripheral blood samples from a lung cancer patient.

Conclusions

It is suggested that our iFMNS approach would be a promising tool for CTCs enrichment and detection in one step.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00860-1.

Nondestructive capture, release, and detection of circulating tumor cells with cystamine-mediated folic acid decorated magnetic nanospheres

Circulating tumor cell (CTC) detection and enumeration have been considered as a noninvasive biopsy method for the diagnosis, characterization, and monitoring of various types of cancers. However, CTCs are exceptionally rare, which makes CTC detection technologically challenging. In the past few decades, much effort has been focused on highly efficient CTC capture, while the activity of CTCs has often been ignored. Here, we develop an effective method for nondestructive CTC capture, release, and detection. Folic acid (FA), as a targeting molecule, is conjugated on magnetic nanospheres through a cleavable disulfide bond-containing linker (cystamine) and a polyethylene glycol (PEG2k) linker, forming MN@Cys@PEG2k-FA nanoprobes, which can bind with folate receptor (FR) positive CTCs specifically and efficiently, leading to the capture of CTCs with an external magnetic field. When approximately 150 and 10 model CTCs were spiked in 1 mL of lysis blood, 93.1 ± 2.9% and 80.0 ± 9.7% CTCs were recovered, respectively. In total, 81.3 ± 2.6% captured CTCs can be released from MN@Cys@PEG2k-FA magnetic nanospheres by treatment with dithiothreitol. The released CTCs are easily identified from blood cells for specific detection and enumeration combined with immunofluorescence staining with a limit of detection of 10 CTC mL-1 lysed blood. Moreover, the released cells remain healthy with high viability (98.6 ± 0.78%) and can be cultured in vitro without detectable changes in morphology or behavior compared with healthy untreated cells. The high viability of the released CTCs may provide the possibility for downstream proteomics research of CTCs; therefore, cultured CTCs were collected for proteomics. As a result, 3504 proteins were identified. In conclusion, the MN@Cys@PEG2k-FA magnetic nanospheres prepared in this study may be a promising tool for early-stage cancer diagnosis and provide the possibility for downstream analysis of CTCs.

Recent Advancements in Nanoparticle-Based Optical Biosensors for Circulating Cancer Biomarkers

The effectiveness of cancer treatment strongly depends on the early detection of the disease. Currently, the most common diagnostic method, tissue biopsy, takes time and can be damaging to the patient. Circulating cancer biomarkers such as circulating tumor DNA, micro-RNA (miRNA), tumor proteins, exosomes, and circulating tumor cells have repeatedly demonstrated their viability as targets for minimally invasive cancer detection through liquid biopsies. However, among other things, achieving a great sensitivity of detection is still challenging due to the very low concentration of biomarkers in fluid samples. This review will discuss how the recent advances in nanoparticle-based biosensors are overcoming these practical difficulties. This report will be focusing mainly on optical transduction mechanisms of metal nanoparticles (M-NPs), quantum dots (QDs), and upconversion nanoparticles (UCNPs).

An efficient strategy for circulating tumor cell detection: surface-enhanced Raman spectroscopy

Circulating tumor cells (CTCs) are circulating cancer cells that shed from tumor tissue into blood vessels and circulate in the blood to invade other organs, which results in fatal metastases. The CTCs in human peripheral blood are the main cause of death in most cancer patients. The detection of CTCs is of great scientific significance and clinical application value for early diagnosis, rapid evaluation of the treatment effect, in vivo drug resistance testing, individualized treatment, tumor recurrence detection and survival time judgment, etc. The surface-enhanced Raman scattering (SERS) method possesses the features of remarkable detection sensitivity, a non-destructive nature, label-free detection, a quick spectrum response and a molecular fingerprint spectrum, which give it great potential in the detection field. In the past decade, SERS technology serving as a bioprobe has been increasingly applied to detect and analyze biological components due to its unique detection advantages. Here, we present an overview of SERS biosensing substrates and recent achievements in detecting CTCs using high-sensitivity SERS platforms, and provide a unique perspective on the design and application of high-performance SERS platforms for CTC detection, especially using non-metal materials.

SERS and fluorescence detection of circulating tumor cells (CTCs) with specific capture-release mode based on multifunctional gold nanomaterials and dual-selective recognition

Herein, a dual-selective recognition and multi-enhanced surface-enhanced Raman scattering (SERS)-fluorescence dual mode detection platform is designed for the detection of circulating tumor cells (CTCs). The gold nanoflowers (AuNFs) substrate was synthesized and the CTCs were captured on the surface area of AuNFs/ITO substrate by aptamers modified. At the same time, the novel nanoprobe was designed, anti-EpCAM (AE) and trigger DNA were modified onto the surface of gold nanostars (AuNSs) through a PEG linker. The novel nanoprobe identified CTCs through the specific recognition reaction between AE and the cell epithelial adhesion molecule of the CTCs. The dual-recognition cellular mechanism of the aptamers and AE improves selectivity. Then, the complementary sequence (CS) hybridize with aptamers to release the captured CTCs into the culture medium. The number of CTCs released was detected by SERS and fluorescence. The limit of SERS detection was 5 cells/mL with a linear relationship from 5 to 200 cells/mL. The limit of fluorescence detection was 10 cells/mL with a linear relationship from 10 to 200 cells/mL. Thus, the developed CTCs detection platform demonstrates promising applications for clinical diagnosis.

Photonic technologies for liquid biopsies: recent advances and open research challenges

The recent development of sophisticated techniques capable of detecting extremely low concentrations of circulating tumor biomarkers in accessible body fluids, such as blood or urine, could contribute to a paradigm shift in cancer diagnosis and treatment. By applying such techniques, clinicians can carry out liquid biopsies, providing information on tumor presence, evolution, and response to therapy. The implementation of biosensing platforms for liquid biopsies is particularly complex because this application domain demands high selectivity/specificity and challenging limit-of-detection (LoD) values. The interest in photonics as an enabling technology for liquid biopsies is growing owing to the well-known advantages of photonic biosensors over competing technologies in terms of compactness, immunity to external disturbance, and ultra-high spatial resolution. Some encouraging experimental results in the field of photonic devices and systems for liquid biopsy have already been achieved by using fluorescent labels and label-free techniques and by exploiting super-resolution microscopy, surface plasmon resonance, surface-enhanced Raman scattering, and whispering gallery mode resonators. This paper critically reviews the current state-of-the-art, starting from the requirements imposed by the detection of the most common circulating biomarkers. Open research challenges are considered together with competing technologies, and the most promising paths of improvement are discussed for future applications.

Prediction of Cancer Stem Cell Fate by Surface-Enhanced Raman Scattering Functionalized Nanoprobes

Cancer stem cells (CSCs) are the fundamental building blocks of cancer dissemination, so it is desirable to develop a technique to predict the behavior of CSCs during tumor initiation and relapse. It will provide a powerful tool for pathological prognosis. Currently, there exists no method of such prediction. Here, we introduce nickel-based functionalized nanoprobe facilitated surface enhanced Raman scattering (SERS) for prediction of cancer dissemination by undertaking CSC-based surveillance. SERS profiling of CSCs of various cell lines (breast cancer, cervical cancer, and lung cancer) was compared with their cancer counterparts for the prediction of prognosis, with statistical significance of single-cell sensitivity. The single-cell sensitivity is critical as even a few CSCs are capable of initiating a tumor. Intermediate states of CSC transmutation to cancer cells and its reverse were monitored, and nanoprobe-assisted SERS profiling was undertaken. We experimentally demonstrated that the quasi-intermediate CSC states have dissimilar profiles during the transformation from cancer to CSC and vice versa enabling statistical differentiation without ambiguity. It was also observed that molecular signatures of these opposite pathways are cancer-type specific. This observation provided additional clarity to the current understanding of relatively unfamiliar quasi-intermediate states; making it possible to predict CSC dissemination for variety of cancers with ∼99% accuracy. Nano probe-based prediction of CSC fate is a powerful prediction tool for ultrasensitive prognosis of malignancy in a complex environment. Such CSC-based cancer prognosis has never been proposed before. This prediction technique has potential to provide insights for cancer diagnosis and prognosis as well as for obtaining information instrumental in designing of meaningful CSC-based cancer therapeutics.

Effect of Varying Expression of EpCAM on the Efficiency of CTCs Detection by SERS-Based Immunomagnetic Optofluidic Device

Simple Summary

In this work we present a magnetically supported SERS-based immunoassay based on solid SERS-active support for the detection of circulating tumor cells. The SERS response in our optofluidic device was correlated with the level of EpCAM expression. The level of EpCAM cell expression in four cell lines with relatively high (human metastatic prostate adenocarcinoma cells (LNCaP)), medium (human metastatic prostate adenocarcinoma cells (LNCaP)), weak (human metastatic prostate adenocarcinoma cells (LNCaP)), and no EpCAM expressions (cervical cancer cells (HeLa) has been estimated using Western Blot method supported by immunochemistry and correlated with responses of immunomagnetic SERS-based analysis. The capture efficiency of developed assay was investigated in metastatic lung cancer patients. The assay demonstrates the capability to detect circulating tumor cells from blood samples over a broad linear range (from 1 to 100 cells/mL) reflecting clinically relevant amount of CTCs depending on the stage of metastasis, age, applied therapy.

Abstract

The circulating tumor cells (CTCs) isolation and characterization has a great potential for non-invasive biopsy. In the present research, the surface–enhanced Raman spectroscopy (SERS)-based assay utilizing magnetic nanoparticles and solid SERS-active support integrated in the external field assisted microfluidic device was designed for efficient isolation of CTCs from blood samples. Magnetic nanospheres (Fe₂O₃) were coated with SERS-active metal and then modified with p-mercaptobenzoic acid (p-MBA) which works simultaneously as a Raman reporter and linker to an antiepithelial-cell-adhesion-molecule (anti-EpCAM) antibodies. The newly developed laser-induced SERS-active silicon substrate with a very strong enhancement factor (up to 10⁸) and high stability and reproducibility provide the additional extra-enhancement in the sandwich plasmonic configuration of immune assay which finally leads to increase the efficiency of detection. The sensitive immune recognition of cancer cells is assisted by the introducing of the controllable external magnetic field into the microfluidic chip. Moreover, the integration of the SERS-active platform and p-MBA-labeled immuno-Ag@Fe₂O₃ nanostructures with microfluidic device offers less sample and analytes demand, precise operation, increase reproducibly of spectral responses, and enables miniaturization and portability of the presented approach. In this work, we have also investigated the effect of varying expression of the EpCAM established by the Western Blot method supported by immunochemistry on the efficiency of CTCs’ detection with the developed SERS method. We used four target cancer cell lines with relatively high (human metastatic prostate adenocarcinoma cells (LNCaP)), medium (human metastatic prostate adenocarcinoma cells (LNCaP)), weak (human metastatic prostate adenocarcinoma cells (LNCaP)), and no EpCAM expressions (cervical cancer cells (HeLa)) to estimate the limits of detection based on constructed calibration curves. Finally, blood samples from lung cancer patients were used to validate the efficiency of the developed method in clinical trials.

Recent advances in microfluidic technologies for circulating tumor cells: enrichment, single-cell analysis, and liquid biopsy for clinical applications

Circulating tumor cells (CTCs) detach from primary or metastatic lesions and circulate in the peripheral blood, which is considered to be the cause of distant metastases. CTC analysis in the form of liquid biopsy, enumeration and molecular analysis provide significant clinical information for cancer diagnosis, prognosis and therapeutic strategies. Despite the great clinical value, CTC analysis has not yet entered routine clinical practice due to lack of efficient technologies to perform CTC isolation and single-cell analysis. Taking the rarity and inherent heterogeneity of CTCs into account, reliable methods for CTC isolation and detection are in urgent demand for obtaining valuable information on cancer metastasis and progression from CTCs. Microfluidic technology, featuring microfabricated structures, can precisely control fluids and cells at the micrometer scale, thus making itself a particularly suitable method for rare CTC manipulation. Besides the enrichment function, microfluidic chips can also realize the analysis function by integrating multiple detection technologies. In this review, we have summarized the recent progress in CTC isolation and detection using microfluidic technologies, with special attention to emerging direct enrichment and enumeration in vivo. Further, few insights into single CTC molecular analysis are also demonstrated. We have provided a review of potential clinical applications of CTCs, ranging from early screening and diagnosis, tumor progression and prognosis, treatment and resistance monitoring, to therapeutic evaluation. Through this review, we conclude that the clinical utility of CTCs will be expanded as the isolation and analysis techniques are constantly improving.

Tumor-cell detection, labeling and phenotyping with an electron-doped bifunctional signal-amplifier

Cancer cell enumeration and phenotyping can predict the prognosis and the therapy efficacy in patients, yet it remains challenging to detect the rare tumor cells. Herein, we report an octopus-inspired, bifunctional aptamer signal amplifier-based cytosensor (OApt-cytosensor) for sensitive cell analysis. By assembling high-affinity antibodies on an electrode surface, the target cells could be specifically captured and thus been sandwiched by the cell surface marker-specific DNA aptamers. These on-cell aptamers function as electrochemical signal amplifiers by base-selective electronic doping with methylene blue. Such a sandwich configuration enables highly sensitive cell detection down to 10 cells/mL (equal to ~1-2 cells at a sampling volume of 150 μL), even in a large excess of nontarget blood cells. This approach also reveals the cell-surface markers and tracks the cellular epithelial-to-mesenchymal transition induced by signaling regulators. Furthermore, the electron-doped aptamer shows remarkable cell fluorescent labeling that guides the release of the captured cells from electrode surface via electrochemistry. These features make OApt-cytosensor a promising tool in revealing the heterogeneous cancer cells and anticancer drug screening at the single-cell level.

SERRS multiplexing with multivalent nanostructures for the identification and enumeration of epithelial and mesenchymal cells

Liquid biopsy represents a new frontier of cancer diagnosis and prognosis, which allows the isolation of tumor cells released in the blood stream. The extremely low abundance of these cells needs appropriate methodologies for their identification and enumeration. Herein we present a new protocol based on surface enhanced resonance Raman scattering (SERRS) gold multivalent nanostructures to identify and enumerate tumor cells with epithelial and mesenchimal markers. The validation of the protocol is obtained with spiked samples of peripheral blood mononuclear cells (PBMC). Gold nanostructures are functionalized with SERRS labels and with antibodies to link the tumor cells. Three types of such nanosystems were simultaneously used and the protocol allows obtaining the identification of all individual tumor cells with the help of a Random Forest ensemble learning method.

Facile Preparation of WO3-x Dots with Remarkably Low Toxicity and Uncompromised Activity as Co-reactants for Clinical Diagnosis by Electrochemiluminescence

The exceptional nature of WO_3-x dots has inspired widespread interest, but it is still a significant challenge to synthesize high-quality WO_3-x dots without using unstable reactants, expensive equipment, and complex synthetic processes. Herein, the synthesis of ligand-free WO_3-x dots is reported that are highly dispersible and rich in oxygen vacancies by a simple but straightforward exfoliation of bulk WS₂ and a mild follow-up chemical conversion. Surprisingly, the WO_3-x dots emerged as co-reactants for the electrochemiluminescence (ECL) of Ru(bpy)₃ ²⁺ with a comparable ECL efficiency to the well-known Ru(bpy)₃ ²⁺ /tripropylamine (TPrA) system. Moreover, compared to TPrA, whose toxicity remains a critical issue of concern, the WO_3-x dots were ca. 300-fold less toxic. The potency of WO_3-x dots was further explored in the detection of circulating tumor cells (CTCs) with the most competitive limit of detection so far.

Sensing Biomarkers with Plasmonics

The detection of biomarkers is critical for enabling early disease diagnosis, monitoring the progression, and tracking the effectiveness of therapeutic intervention. Plasmonic sensors exhibit a broad range of analytical capabilities, from the rapid generation of colorimetric readouts to single-molecule sensitivity in ultralow sample volumes, which have led to their increased exploration in bioanalysis and point-of-care applications. This perspective presents selected accounts of recent developments on the different types of plasmonic sensing platforms, the pervasive challenges, and outlook on the pathway to translation. We highlight the sensing of upcoming biomarkers, including microRNA, circulating tumor cells, exosomes, and cell-free DNA, and discuss the opportunity of utilizing plasmonic nanomaterials and tools for biomarker detection beyond biofluids, such as in tissues, organs, and disease sites. The integration of plasmonic biosensors with established and upcoming technologies of instrumentation, sample pretreatment, and data analysis will help realize their translation to clinical settings for improving healthcare and enhancing the quality of life.

Graphene and Graphene Oxide Applications for SERS Sensing and Imaging

Surface Enhanced Raman Spectroscopy (SERS) has a long history as an ultrasensitive platform for the detection of biological species from small aromatic molecules to complex biological systems as circulating tumor cells. Thanks to unique properties of graphene, the range of SERS applications has largely expanded. Graphene is efficient fluorescence quencher improving quality of Raman spectra. It contributes also to the SERS enhancement factor through the chemical mechanism. In turn, the chemical flexibility of Reduced Graphene Oxide (RGO) enables tunable adsorption of molecules or cells on SERS active surfaces. Graphene oxide composites with SERS active nanoparticles have been also applied for Raman imaging of cells. This review presents a survey of SERS assays employing graphene or RGO emphasizing the improvement of SERS enhancement brought by graphene or RGO. The structure and physical properties of graphene and RGO will be discussed too.