Gold nanoparticles labeling with hybridization chain reaction amplification strategy for the sensitive detection of HepG2 cells by inductively coupled plasma mass spectrometry

Genetically engineered virus-like particle-armoured and multibranched DNA scaffold-corbelled ultra-sensitive hierarchical hybridization chain reaction for targeting-enhanced imaging in living biosystems under spatiotemporal light powering

Although nucleic acids-based fluorescent biosensors, exemplified by the hybridization chain reaction (HCR), have exhibited promise as an imaging tool for detecting disease-related biomolecular makers in living biosystems, they still face certain challenges. These include the need for improved sensitivity, poor bio-targeting capability, the absence of signal enrichment interface and the uncontrollable biosensing initiation. Herein, we present a range of effective solutions. First, a stacking design resembling building blocks is used to construct a special hierarchical HCR (termed H-HCR), for which a hierarchical bridge is employed to graft multiunit HCR products. Furthermore, the H-HCR components are encapsulated into a virus-like particle (VLP) endowed with a naturally peptide-mediated targeting unit through genetic engineering of plasmids, after which the biosensor can specifically identify cancer cytomembranes. By further creating a multibranched DNA scaffold to enrich the H-HCR produced detection signals, the biosensor's analyte recognition module is inserted with a photocleavage-linker, allowing that the biosensing process can be spatiotemporally initiated via a light-powered behavior. Following these innovations, this genetically engineered VLP-armoured and multibranched DNA-scaffold-corbelled H-HCR demonstrates an ultra-sensitive and specific biosensing performance to a cancer-associated microRNA marker (miRNA-155). Beyond the worthy in vitro analysis, our method is also effective in performing imaging assays for such low-abundance analyte in living cells and even bodies, thus providing a roust platform for disease diagnosis.

Ultrasensitive reporter DNA sensors built on nucleic acid amplification techniques: Application in the detection of trace amount of protein

The detection of protein is of great significance for the study of biological physiological function, early diagnosis of diseases and drug research. However, the sensitivity of traditional protein detection methods for detecting trace amount of proteins was relatively low. By integrating sensitive nucleic acid amplification techniques (NAAT) with protein detection methods, the detection limit of protein detection methods can be substantially improved. The DNA that can specifically bind to protein targets and convert protein signals into DNA signals is collectively referred to reporter DNA. Various NAATs have been used to establish NAAT-based reporter DNA sensors. And according to whether enzymes are involved in the amplification process, the NAAT-based reporter DNA sensors can be divided into two types: enzyme-assisted NAAT-based reporter DNA sensors and enzyme-free NAAT-based reporter DNA sensors. In this review, we will introduce the principles and applications of two types of NAAT-based reporter DNA sensors for detecting protein targets. Finally, the main challenges and application prospects of NAAT-based reporter DNA sensors are discussed.

GPNMB+ Gal-3+ hepatic parenchymal cells promote immunosuppression and hepatocellular carcinogenesis

Hepatocellular carcinoma (HCC) formation is a multi-step pathological process that involves evolution of a heterogeneous immunosuppressive tumor microenvironment. However, the specific cell populations involved and their origins and contribution to HCC development remain largely unknown. Here, comprehensive single-cell transcriptome sequencing was applied to profile rat models of toxin-induced liver tumorigenesis and HCC patients. Specifically, we identified three populations of hepatic parenchymal cells emerging during HCC progression, termed metabolic hepatocytes (HCMeta ), Epcam+ population with differentiation potential (EP+Diff ) and immunosuppressive malignant transformation subset (MTImmu ). These distinct subpopulations form an oncogenic trajectory depicting a dynamic landscape of hepatocarcinogenesis, with signature genes reflecting the transition from EP+Diff to MTImmu . Importantly, GPNMB+ Gal-3+ MTImmu cells exhibit both malignant and immunosuppressive properties. Moreover, SOX18 is required for the generation and malignant transformation of GPNMB+ Gal-3+ MTImmu cells. Enrichment of the GPNMB+ Gal-3+ MTImmu subset was found to be associated with poor prognosis and a higher rate of recurrence in patients. Collectively, we unraveled the single-cell HCC progression atlas and uncovered GPNMB+ Gal-3+ parenchymal cells as a major subset contributing to the immunosuppressive microenvironment thus malignance in HCC.

Target-triggered enzyme-free amplification for highly efficient AND-gated bioimaging in living cells

Rapid, simultaneous, and sensitive detection of biomolecules has important application prospects in disease diagnosis and biomedical research. However, because the content of intracellular endogenous target biomolecules is usually very low, traditional detection methods can't be used for effective detection and imaging, and to enhance the detection sensitivity, signal amplification strategies are frequently required. The hybridization chain reaction (HCR) has been used to detect many disease biomarkers because of its simple operation, good reproducibility, and no enzyme involvement. Although HCR signal amplification methods have been employed to detect and image intracellular biomolecules, there are still false positive signals. Therefore, a target-triggered enzyme-free amplification system (GHCR system) was developed, as a fluorescent AND-gated sensing platform for intracellular target probing. The false positive signals can be well avoided and the accuracy of detection and imaging can be improved by using the design of the AND gate. Two cancer markers, GSH and miR-1246, were used as two orthogonal inputs for the AND gated probe. The AND-gated probe only works when GSH and miR-1246 are the inputs at the same time, and FRET signals can be the output. In addition to the use of AND-gated imaging, FRET-based high-precision ratiometric fluorescence imaging was employed. FRET-based ratiometric fluorescent probes have a higher ability to resist interference from the intracellular environment, they can avoid false positive signals well, and they are expected to have good specificity. Due to the advantages of HCR, AND-gated, and FRET fluorescent probes, the GHCR system exhibited highly efficient AND-gated FRET bioimaging for intracellular endogenous miRNAs with a lower detection limit of 18 pM, which benefits the applications of ratiometric intracellular biosensing and bioimaging and offers a novel concept for advancing the diagnosis and therapeutic strategies in the field of cancer.

Ultrasensitive determination of β-conglutin food allergen by means an aptamer assay based on inductively coupled plasma mass spectrometry detection

The overall objective of this work is the evaluation of different competitive aptamer assays based on inductively coupled plasma mass spectrometry (ICP-MS) detection for the determination of β-conglutin (food protein allergen from lupin) in flour samples. To this end, two competitive aptamer assay schemes were developed using either thiolated aptamers chemisorbed onto gold nanoparticles (AuNPs) or biotinylated aptamers linked to streptavidin-AuNPs. The influence of ICP-MS detection mode (i.e., conventional vs single particle) on assay performance was explored. In the case of the thiolated aptamer, the limit of detection (LoD) obtained using the single particle mode was improved 2-fold as compared to the LoD provided by the conventional mode. With regards to the biotinylated aptamer, the use of the conventional mode provided a 5-fold improvement of LoD as compared to that obtained for the single particle one. Using the optimized conditions, the best LoD of 2 pM was obtained with the biotinylated aptamer operating with conventional ICP-MS detection. When compared to previous reports using the same aptamer in a competitive assay, the developed method significantly improved the LoD by at least an order of magnitude. Different flour samples containing lupin were successfully analyzed according to European Conformity guidelines for the analysis of food contaminants.

Ultrasensitive PEC cytosensor for breast cancer cells detection and inhibitor screening based on plum-branched CdS/Bi2S3 heterostructures

Breast cancer is the most common malignant tumor in women, which seriously threatens the life and health of patients. Therefore, facile and sensitive detection of human breast cancer cells is crucial for cancer diagnosis. In this work, plum-branched CdS/Bi₂S₃ heterostructures (CdS/Bi₂S₃ HSs) were synthesized under hydrothermal condition, whose photoelectrochemical (PEC) property and biocompatibility were scrutinously investigated. In parallel, a signal amplification strategy was designed based on immune recognition between epidermal growth factor receptor (EGFR) overexpressed on membrane of breast cancer cells MDA-MB-231 and its aptamer. Integration of the above together, a highly sensitive PEC cytosensor was developed for analysis of target MDA-MB-231 cells, exhibiting a wider linear range of 1 × 10² ∼ 3 × 10⁵ cells mL^-1 with a limit of detection (LOD) down to 6 cells mL^-1 (S/N = 3). Further, the biosensor was explored for anticancer drug (e.g., dacomitinib) screening by monitoring the variations in the PEC signals of the expressed EGFR upon drug stimulation. The obtained CdS/Bi₂S₃ HSs are identified as promising and feasible photoactive material for determination of cancer cells and drug screening in clinic and related research.

Gold Nanostars Combined with the Searched Antibody for Targeted Oral Squamous Cell Carcinoma Therapy

Oral squamous cell carcinoma (OSCC) is the most common cancer in the oral and maxillofacial region. Due to the special physiological and anatomical position of the oral cavity, the disease often has a significant impact on the chewing, swallowing, language, and breathing functions of patients. In recent years, with the development of medical molecular biology, molecular targeted therapy has received increasing clinical attention and has gradually become a new method for the treatment of malignant tumors. In this research, gold nanostars with a high photothermal effect combined with the searched targeted antibody were used for OSCC therapy. We use the data set in the public database and construct a gene co-expression module by weighted gene co-expression network analysis (WGCNA). It was found that the turquoise module and the midnight blue module had the greatest connection to tumorigenesis. Cytoscape software was used to analyze the important modules, and the top 10 genes of each module were selected; the survival analysis of the top 10 genes was carried out by gene expression profiling interactive analysis (GEPIA), which indicated that these genes (SERPINH1, MMP11, ADAM12, FADS3, SLC36A2, C1QTNF7, SCRG1, and APOBEC2) have statistical significance as key genes that are related to the tumorigenesis of OSCC. Then, the anti-SERPINH1 antibody targeted to SERPINH1 was chosen as the inhibitor and combined with gold nanostars for photothermal assisted targeted therapy. Thus, the searched key genes can be regarded as biomarkers and therapeutic targets for further precise diagnosis.

Water-Dispersible Gold Nanoclusters: Synthesis Strategies, Optical Properties, and Biological Applications

Atomically precise gold nanoclusters (AuNCs) are an emerging class of quantum-sized nanomaterials. Intrinsic discrete electronic energy levels have endowed them with fascinating electronic and optical properties. They have been widely applied in the fields of optoelectronics, photovoltaics, catalysis, biochemical sensing, bio-imaging, and therapeutics. Nevertheless, most AuNCs are synthesized in organic solvents and do not disperse in aqueous solutions; this restricts their biological applications. In this review, we focus on the recent progress in the preparation of water-dispersible AuNCs and their biological applications. We first review different methods of synthesis, including direct synthesis from hydrophilic templates and indirect phase transfer of hydrophobic AuNCs. We then discuss their photophysical properties, such as emission enhancement and fluorescence lifetimes. Next, we summarize their latest applications in the fields of biosensing, biolabeling, and bioimaging. Finally, we outline the challenges and potential for the future development of these AuNCs.

NIR II Light-Response Au Nanoframes: Amplification of a Pressure- and Temperature-Sensing Strategy for Portable Detection and Photothermal Therapy of Cancer Cells

Quantitative detection of cancer cells using portable devices is promising for the development of simple, fast, and point-of-care cancer diagnostic techniques. However, how to further amplify the detection signal to improve the sensitivity and accuracy of detecting cancer cells by portable devices remains a challenge. To solve the problem, we, for the first time, synthesized folic-acid-conjugated Au nanoframes (FA-Au NFs) with amplification of pressure and temperature signals for highly sensitive and accurate detection of cancer cells by portable pressure meters and thermometers. The resulting Au NFs exhibit excellent near-infrared (NIR) photothermal performance and catalase activity, which can promote the decomposition of NH₄HCO₃ and H₂O₂ to generate corresponding gases (CO₂, NH₃, and O₂), thereby synergistically amplifying pressure signals in a closed reaction vessel. At the same time, Au NFs with excellent peroxidase-like activity can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce TMB oxide (oxTMB) with a strong photothermal effect, thereby cooperating with Au NFs to amplify the photothermal signal. In the presence of cancer cells with overexpressing folate receptors (FRs), the molecular recognition signals between FA and FR can be converted into amplified pressure and temperature signals, which can be easily read by portable pressure meters and thermometers, respectively. The detection limits for cancer cells using pressure meters and thermometers are 6 and 5 cells/mL, respectively, which are better than other reported methods. Moreover, such Au NFs can improve tumor hypoxia by catalyzing the decomposition of H₂O₂ to produce O₂ and perform photothermal therapy of cancer. Together, our work provides new insight into the application of Au NFs to develop a dual-signal sensing platform with amplification of pressure and temperature signals for portable and ultrasensitive detection of cancer cells as well as personalized cancer therapy.

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.

Hybridization chain reaction and its applications in biosensing

To pursue the sensitive and efficient detection of informative biomolecules for bioanalysis and disease diagnosis, a series of signal amplification techniques have been put forward. Among them, hybridization chain reaction (HCR) is an isothermal and enzyme-free process where the cascade reaction of hybridization events is initiated by a target analyte, yielding a long nicked dsDNA molecule analogous to alternating copolymers. Compared with conventional polymerase chain reaction (PCR) that can proceed only with the aid of polymerases and complicated thermal cycling, HCR has attracted increasing attention because it can occur under mild conditions without using enzymes. As a powerful signal amplification tool, HCR has been employed to construct various simple, sensitive and economic biosensors for detecting nucleic acids, small molecules, cells, and proteins. Moreover, HCR has also been applied to assemble complex nanostructures, some of which even act as the carriers to execute the targeted delivery of anticancer drugs. Recently, HCR has engendered tremendous progress in RNA imaging applications, which can not only achieve endogenous RNA imaging in living cells or even living animals but also implement imaging-guided photodynamic therapy, paving a promising path to promote the development of theranostics. In this review, we begin with the fundamentals of HCR and then focus on summarizing the recent advances in HCR-based biosensors for biosensing and RNA imaging strategies. Further, the challenges and future perspective of HCR-based signal amplification in biosensing and theranostic application are discussed.

Highly Sensitive and Specific Mass Spectrometric Platform for miRNA Detection Based on the Multiple-Metal-Nanoparticle Tagging Strategy

The multiple-metal-nanoparticle tagging strategy has generally been applied to the multiplexed detection of multiple analytes of interest such as microRNAs (miRNAs). Herein, it was used for the first time to improve both the specificity and sensitivity of a novel mass spectroscopic platform for miRNA detection. The mass spectroscopic platform was developed through the integration of the ligation reaction, hybridization chain reaction amplification, multiple-metal-nanoparticle tagging, and inductively coupled plasma mass spectrometry. The high specificity resulted from the adoption of the ligation reaction is further enhanced by the multiple-metal-nanoparticle tagging strategy. The combination of hybridization chain reaction amplification and metal nanoparticle tagging endows the proposed platform with the feature of high sensitivity. The proposed mass spectrometric platform achieved quite satisfactory quantitative results for Let-7a in real-world cell line samples with accuracy comparable to that of the real-time quantitative reverse-transcriptase polymerase chain reaction method. Its limit of detection and limit of quantification for Let-7a were experimentally determined to be about 0.5 and 10 fM, respectively. Furthermore, due to the unique way of utilizing the multiple-metal-nanoparticle tagging strategy, the proposed platform can unambiguously discriminate between the target miRNA and nontarget ones with single-nucleotide polymorphisms based on their response patterns defined by the relative mass spectral intensities among the multiple tagged metal elements and can also provide location information of the mismatched bases. Its unique advantages over conventional miRNA detection methods make the proposed platform a promising and alternative tool in the fields of clinical diagnosis and biomedical research.

Signal amplification strategies for clinical biomarker quantification using elemental mass spectrometry

The current trends in modern medicine towards early diagnosis, or even prognosis, of different diseases have brought about the need for the corresponding biomarker detection at ever lower levels in really complex matrices. To do so, it is necessary to use proper extremely sensitive detection techniques such as elemental mass spectrometry. However, target labelling with metals for subsequent sensitive ICP-MS detection falls short nowadays even if resorting to inorganic nanoparticles containing a high number of detectable elements. Thus, new amplification strategies are being proposed to face this analytical challenge that will be critically discussed in this paper. Fundamentals of different novel strategies developed to achieve signal amplification and sensitive elemental mass spectrometry detection are here discussed. Some representative examples of relevant clinical applications are highlighted, along with future prospects and challenges.

Composition of Intracellular Protein Corona around Nanoparticles during Internalization

It has been well established that the early-stage interactions of nanoparticles with cells are governed by the extracellular protein corona. However, after entering into the cells, the evolving protein corona is the key to subsequent processing of nanoparticles by cells. To identify the protein corona around intracellular nanoparticles, it is essential to maintain its original compositions during cell treatment. Herein, we develop a paraformaldehyde (PFA) cross-linking strategy to stabilize corona compositions when extracting protein coronas from cells, providing original information on protein coronas around intercellular gold nanoparticles (AuNPs). The stability of the protein corona after PFA cross-linking was carefully investigated with several characterization methods, and the results demonstrate that PFA cross-linking successfully prevents the dissociation and exchange of corona proteins. Then the recovered intracellular protein corona around AuNPs from living HepG2 cells with a PFA cross-linking strategy was subjected to nanoHPLC-MS/MS for proteomic analysis. It was found that the compositions of intracellular protein coronas are dominated by cell-derived proteins and undergo significant variation of protein species and amounts over time during internalization. Time-resolved analysis provides relevant proteins involved in nanoparticle cellular uptake and transportation, indicating that AuNPs are endocytosed mainly by a clathrin-mediated uptake mechanism and directed into an endolysosomal pathway toward their final destination. Such proteomic-based results are verified by pharmacological inhibition and TEM imaging analysis. This work provides a universal strategy to study compositions of protein corona around intercellular nanoparticles and could be a footstone to link the formation of protein corona around nanoparticles to their biological function in cells.

Homogeneous assay based on the pre-reduction and selective cation exchange for detection of multiple targets by atomic spectrometry

In view of the high sensitivity and good selectivity, chemical vapor generation atomic spectrometry (CVG-AS) and inductively coupled plasma mass spectrometer (ICP-MS), especially low-cost atomic fluorescence spectrometry (AFS) have been widely used in bioassay. However, the existing AS method is mostly based on heterogeneous strategies, and can't detect multiple targets in one system. In this study, we present the discovery and mechanism study of a phenomenon of Hg²⁺ pre-reduction that the concentration of Hg²⁺ decreased when it was mixed with the reductants (ascorbic acid (AA), SnCl₂, or NaBH₄/KBH₄) over long-time reaction (hours) by CVG-AFS and ICP-MS. A homogeneous Cu²⁺ assay method was developed based on the competition reaction of Cu²⁺ and Hg²⁺ for consuming AA, and its application in the detection of pyrophosphate (PPi) and alkaline phosphatase (ALP) was investigated based on the PPi complexation with Cu²⁺, and ALP hydrolyzation of PPi using CVG-AFS as a representative detector. Subsequently, in order to further verify the applicability of the system, cation exchange reaction (CER) was utilized here based on the selectively recognize Ag⁺ and C-Ag⁺-C by CuS nanoparticles (NPs). As the exchanged Cu²⁺ from CuS NPs can be sensitively and selectively detected via above-mentioned Cu²⁺ assay method, this strategy can be extended for the Ag⁺, DNA and prostate specific antigen (PSA) detection based on base complementary pairing and the specific recognition of aptamer. Under the optimal experimental conditions, the system showed high sensitivity for the detection of Cu²⁺, PPi, ALP, Ag⁺, DNA, and PSA, with limit of detections (LODs) of 0.12 nmol L^-1, 25 μmol L^-1, 0.025 U/L, 0.2 nmol L^-1, 0.05 nmol L^-1, and 0.03 ng/mL, respectively. The method was successfully used to determination Cu²⁺, ALP, and PSA in human serums, showing similar results with those of ICP-MS and kits methods.

The Recent Development of Hybridization Chain Reaction Strategies in Biosensors

With the continuous development of biosensors, researchers have focused increasing attention on various signal amplification strategies to pursue superior performance for more applications. In comparison with other signal amplification strategies, hybridization chain reaction (HCR) as a powerful signal amplification technique shows its certain charm owing to nonenzymatic and isothermal features. Recently, on the basis of conventional HCR, this technique has been developed and improved rapidly, and a variety of HCR-based biosensors with excellent performance have been reported. Herein, we present a systematic and critical review on the research progress of HCR in biosensors in the last five years, including the newly developed HCR strategies such as multibranched HCR, migration HCR, localized HCR, in situ HCR, netlike HCR, and so on, as well as the combination strategies of HCR with isothermal signal amplification techniques, nanomaterials, and functional DNA molecules. By illustrating some representative works, we also summarize the advantage and challenge of HCR in biosensors, and offer a deep discussion of the latest progress and future development trends of HCR in biosensors.

Colorimetric nanoplatform for visual determination of cancer cells via target-catalyzed hairpin assembly actuated aggregation of gold nanoparticles

According to aptamer-mediated hairpin DNA cascade amplifier and gold nanoparticles aggregation, an optical platform for cancer cells determination has been proposed. High-affinity chimeric aptamers were used for cancer cell detection and also as an initiator for beginning hairpin assembly to construct three-way junction (3WJ) nanostructures. These three hairpins were modified at 3' ends with biotin. In the presence of target cell, chimeric aptamer binds to its ligand on cell surface and initiates 3WJ nanostructures formation. These 3WJ nanostructures interact with streptavidin-modified gold nanoparticles (AuNPs) via non-covalent biotin-streptavidin interactions and create a crossover lattice of nanoparticles. This event leads to AuNPs aggregation and red-shifting. The results were confirmed by gel electrophoresis and UV-visible spectrophotometry. The dynamic range of this assay is 25 to 10⁷ cells with a detection limit of 10 cells which is respectively 9 and 4 times more significant than the sensitivity of AuNP-based approaches without amplification and enzyme-mediated signal amplification. Graphical abstract.

Double signal amplification strategy for ultrasensitive electrochemical biosensor based on nuclease and quantum dot-DNA nanocomposites in the detection of breast cancer 1 gene mutation

Rapid and efficient detection of microRNA (miRNA) of breast cancer 1 gene mutation (BRCA1) at their earliest stages is one of the crucial challenges in cancer diagnostics. In this study, a highly-sensitive electrochemical DNA biosensor was fabricated by double signal amplification (DSA) strategy for the detection of ultra-trace miRNA of BRCA1. In the presence of target miRNA of BRCA1, the well-matched RNA-DNA duplexes were specifically recognized by double-strand specific nuclease (DSN), and the DNA part of the duplexes were then cleaved and miRNAs were released to trigger another following cycle, which produced a primarily amplified signal by such a cyclic enzymatic signal amplification (CESA). Then triple-CdTe quantum dot labelled DNA nanocomposites (3-QD@DNA NC) was selectively hybridized with the cleaved DNA probe on the electrode and produced multiply amplified signals. The biosensor exhibited a high sensitivity for the detection of miRNA of BRCA1 in concentrations ranging from 5 aM to 5 fM, and its detection limit of 1.2 aM was obtained, which is two or three orders of magnitude lower than those by single signal amplification strategy such as CESA or QD-labeled DNA probes. The as-prepared biosensor was successfully used to detect the miRNA of BRCA1 in human serum samples with acceptable stability, good reproducibility, and good recovery. The proposed DNA biosensor based on double signal amplification strategy provided a feasible, rapid, and sensitive platform for early clinical diagnosis and practical applications.

Simultaneous determination of two phosphorylated p53 proteins in SCC-7 cells by an ICP-MS immunoassay using apoferritin-templated europium(III) and lutetium(III) phosphate nanoparticles as labels

Phosphorylated p53 proteins are biomarkers with clinical utility for early diagnosis of cancer, but difficult to quantify. An inductively coupled plasma mass spectrometry (ICP-MS) based immunoassay is described here that uses uniform lanthanide nanoparticles (NPs) as elemental tags for the simultaneous determination of two phosphorylated p53 proteins. Apoferritin templated europium (Eu) phosphate (AFEP) NPs and apoferritin templated lutetium (Lu) phosphate (AFLP) NPs with 8 nm in diameter were used to label two phosphorylated p53 proteins at serine 15 and serine 392 sites (p-p53¹⁵ and p-p53³⁹²), respectively. The assay has a sandwich format, and p-p53¹⁵ and p-p53³⁹² were first captured and then recognized by AFEP and AFLP NPs labelled antibodies, respectively. The Eu and Lu were then released from the immune complexes under acidic condition for ICP-MS measurement. The limits of detection for p-p53¹⁵ and p-p53³⁹² are 200 and 20 pg·mL^-1, with linear ranges of 0.5-20 and 0.05-20 ng·mL^-1, respectively. The method was further applied to study the response of p-p53¹⁵ and p-p53³⁹² in SCC-7 cells exposed to the natural carcinogen arsenite. A significant up-regulation of p-p53¹⁵ and p-p53³⁹² can be observed when cells were exposed to arsenite at 5 μmol·L^-1 level for 24 h. Graphical abstract Schematic presentation of the ICP-MS immunoassay using apoferritin templated europium (III) and lutetium (III) phosphate nanoparticles as labels for the simultaneous determination of two phosphorylated p53 proteins. Europium (Eu) phosphate nanoparticles (blue) and lutetium (Lu) phosphate nanoparticles (pink) were synthesized in the size-restricted cavity of apoferritin. They were further coupled with antibodies to prepare Eu and Lu labelled probes for p-p53¹⁵ (blue) and p-p53³⁹² (pink), respectively. After formation of a a sandwich, the labelled Eu and Lu were dissociated in acid and then introduced to ICP-MS for the simultaneous determination of two phosphorylated p53 proteins p-p53¹⁵ (blue) and p-p53³⁹² (pink).

Cellular interface supported toehold strand displacement cascade for amplified dual-electrochemical signal and its application for tumor cell analysis

In this work, toehold strand displacement cascade (TSDC) has been delicately designed and carried out on the cellular interface for the amplification and output of dual-electrochemical signal. Specifically, antibody cross-linked T strand can recognize cell which is linked with immune-magnetic bead. Subsequently, T strand on the cellular interface can mediate the occurrence of TSDC, resulting the change of SN₃/S1-MB to SN₃/S2-Fc ratio in the supernatant after magnetic separation. The resultant SN₃/S1-MB and SN₃/S2-Fc can be immobilized on the electrode interface through click chemistry and give the amplified double electrochemical signal. So the tumor cell amount can closely correlate with the change of the double signal. Except for output of the double signal for improvement of analytical accuracy, the double magnetic separation not only eliminate the interference of the complicated substances in serum, but also remove the influence of cell on click reaction on the electrode interface. So based on cellular interface supported TSDC for amplified dual-electrochemical signal, the established method has been successfully applied to analyze the tumor cells in serum accurately and sensitively.

A light-up fluorescence assay for tumor cell detection based on bifunctional split aptamers

Light-up aptamers have attracted growing attention due to their advantages of being label-free and having low fluorescence background. In this work, we developed a light-up fluorescence assay for label-free detection of tumor cells based on a bifunctional split aptamer (BFSA) that contained two DNA strands (BFSA-a and BFSA-b). BFSA-a and BFSA-b were constructed by combining aptamers ZY11 and ThT.2-2, which could specifically bind to the tumor cell SMMC-7721 and activate the fluorescence of thioflavin T (ThT). A Helper strand was introduced to hybridize with BFSA-b, and then BFSA-a and BFSA-b were separated if the target cell was absent. Only when the target cell is present can BFSA-a approach and hybridize with BFSA-b due to the 'induced-fit effect', which made the Helper strand dissociate. Then ThT bound to BFSA and the fluorescence of ThT was activated. The results indicated that this fluorescence assay had a good linear response to the target cells in the range of 250-20 000 cells in 100 μL binding buffer; the lowest cell number actually detected was 125 cells in 100 μL buffer. This assay also displayed excellent selectivity and was successfully applied to detect target cells in 20% human serum samples. The design of bifunctional split aptamers realized no-washing, label-free, low-cost, one-step detection of tumor cells, which could generate detectable fluorescence signals just by mixing nucleic acid aptamers and fluorescent reporter molecules with target cells. Such a design of aptamer probes also has the potential to construct stimuli-responsive controlled drug delivery systems.

Enzyme-free amplified DNA assay: five orders of linearity provided by metal stable isotope detection

For the quantification of mutated genes at greatly varied concentrations in body fluids, nucleic acid amplification strategies are often challenged by limited dynamic linear ranges. The proposed metal stable isotope detection strategy demonstrates five orders of linear range and a lower attomol detection limit, showing promising potential in clinical diagnosis.

Applications of Gold Nanoparticles in Non-Optical Biosensors

Due to their unique properties, such as good biocompatibility, excellent conductivity, effective catalysis, high density, and high surface-to-volume ratio, gold nanoparticles (AuNPs) are widely used in the field of bioassay. Mainly, AuNPs used in optical biosensors have been described in some reviews. In this review, we highlight recent advances in AuNP-based non-optical bioassays, including piezoelectric biosensor, electrochemical biosensor, and inductively coupled plasma mass spectrometry (ICP-MS) bio-detection. Some representative examples are presented to illustrate the effect of AuNPs in non-optical bioassay and the mechanisms of AuNPs in improving detection performances are described. Finally, the review summarizes the future prospects of AuNPs in non-optical biosensors.

Ultrasensitive analysis of heat shock protein 90α with antibodies orderly arrayed on a novel type of immunoprobe based on magnetic COFs

The early diagnosis of liver cancer by target biomarkers is of great significance for improving the survival rate of cancer patients. However, it is still a challenging task to sensitively detect circulating protein biomarkers due to decreased binding activity of antibodies originating from uncontrolled orientation of immobilization on the surface of a solid matrix. In this work, a novel immunoaffinity probe, Fe₃O₄@TpBD-DSS-Ab-MEG, based on magnetic COFs with ordered arrangement of anchored antibodies has been developed and applied for the first time to detection of a cancer biomarker, heat shock protein 90alpha (Hsp90α). The fabricated composites possess favorable features from magnetic cores and COF shells, including strong magnetic responses (7.96 emu g^-1), ordered active groups, a large amount of immobilized antibodies (111.7 μg/mg), good solvent and thermal stability. Fe₃O₄@TpBD-DSS-Ab-MEG demonstrated low detection limit (50 pg/mL), high selectivity (Hsp90α:BSA = 1:1000), desirable repeatability and good stability for Hsp90α immunocapture. Compared with other immunoprobes, our materials showed higher selectivity and sensitivity, which were mainly attributed to regular arrays of surface antibodies. Furthermore, samples containing Hsp90α at the concentration of 1 µg/mL in human plasma were used to test our immunoprobe, and 2 peptides of Hsp90α were successfully observed. The proposed non-invasive immunoassay strategy offers enhanced ability to control the orientation of immobilized antibodies and great promise for accurate analysis of the liver cancer biomarker Hsp90α in a complicated biological matrix. In addition, the facile preparation of magnetic COFs support and the satisfactory analytical performance made the newly developed immunoprobe a potential tool for sensitive detection of other cancer biomarkers in clinical diagnosis.

A DNA nanostructured aptasensor for the sensitive electrochemical detection of HepG2 cells based on multibranched hybridization chain reaction amplification strategy

Sensitive detection of cancer cells is beneficial to the early diagnosis of cancer and individual treatment. In the present study, a DNA nanostructured aptasensor was used for the sensitive electrochemical detection of human liver hepatocellular carcinoma cells (HepG2) based on multibranched hybridization chain reaction amplification strategy. We established a well-designed platform by immobilizing DNA tetrahedron, a three-dimensional DNA nanostructure, on the gold electrode to capture HepG2 cells more specifically and efficiently. Meanwhile, functional hybrid nanoprobes consisted of MIL-101@AuNPs (Au nanoparticles), numerous hemin/G-quadruplex DNAzyme from multibranched hybridization chain reaction, and natural horseradish peroxidase (HRP) was designed. The hybrid nanoprobes possessed the functions of specific discernment and enzymatic signal amplification simultaneously. With the help of nanoprobes, HepG2 cells were recognized and captured to form a DNA tetrahedron-cell-nanoprobe sandwich-like structure on the electrode surface. The lower detection limit of this established cytosensor is 5 cells per ml. Moreover, it delivered a broad detection range from 10² to 10⁷ cells per ml. The results revealed that the as-proposed cytosensor may be utilized as a powerful tool for early diagnosis of cancer in the future.

Current Advances in Aptamers for Cancer Diagnosis and Therapy

Nucleic acid aptamers are single-stranded oligonucleotides that interact with target molecules with high affinity and specificity in unique three-dimensional structures. Aptamers are generally isolated by a simple selection process called systematic evolution of ligands by exponential enrichment (SELEX) and then can be chemically synthesized and modified. Because of their high affinity and specificity, aptamers are promising agents for biomarker discovery, as well as cancer diagnosis and therapy. In this review, we present recent progress and challenges in aptamer and SELEX technology and highlight some representative applications of aptamers in cancer therapy.

Gold Nanoparticle Based Platforms for Circulating Cancer Marker Detection

Detection of cancer-related circulating biomarkers in body fluids has become a cutting-edge technology that has the potential to noninvasively screen cancer, diagnose cancer at early stage, monitor tumor progression, and evaluate therapy responses. Traditional molecular and cellular detection methods are either insensitive for early cancer intervention or technically costly and complicated making them impractical for typical clinical settings. Due to their exceptional structural and functional properties that are not available from bulk materials or discrete molecules, nanotechnology is opening new horizons for low cost, rapid, highly sensitive, and highly specific detection of circulating cancer markers. Gold nanoparticles have emerged as a unique nanoplatform for circulating biomarker detection owning to their advantages of easy synthesis, facile surface chemistry, excellent biocompatibility, and remarkable structure and environment sensitive optical properties. In this review, we introduce current gold nanoparticle-based technology platforms for the detection of four major classes of circulating cancer markers - circulating tumor cells, vesicles, nucleic acids, and proteins. The techniques will be summarized in terms of signal detection strategies. Distinctive examples are provided to highlight the state-of-the-art technologies that significantly advance basic and clinical cancer research.