Homogeneous Multiplex Immunoassay for One-Step Pancreatic Cancer Biomarker Evaluation

Highly sensitive detection of aflatoxin B1 byCRISPR/Cas12a-assisted single nanoparticle counting

CRISPR (clustered regularly interspaced short palindromic repeats) and CRISPR-associated protein (Cas) have gained extensive applications in bioassays. However, CRISPR-based detection platforms are often hampered by limited analytical sensitivity, while nucleic acid-based amplification strategies are usually indispensable for additional signal enhancement with potential risks of amplification leakages. To address these challenges, an amplification-free CRISPR-based bioassay of aflatoxin B1 (AFB1) was proposed by applying single nanoparticle counting. Single-particle mode inductively coupled plasma mass spectrometry (Sp-ICPMS) has been regarded as a sensitive tool for nanoparticle counting since one nanoparticle can generate considerable signals above backgrounds. With AFB1, activator strands were introduced to initiate the trans-cleavage of CRISPR/Cas12a for cutting the nanoparticles-tagged-magnetic beads, which were transduced to nanoparticle count signals after separation. Finally, a pico-mole level limit-of-detections (LODs) with moderate selectivity was achieved. Certified reference materials (CRMs) analysis and recovery tests were conducted with promising results. To our best knowledge, this is the first report of the single particle counting-based CRISPR/Cas12a biosensing study.

Integrating aptasensor with an explosive mass-tag signal amplification strategy for ultrasensitive and multiplexed analysis using a miniature mass spectrometer

Mass probes attached with aptamers and mass tags offer excellent specificity and sensitivity for multiplexed detection, wherein the dissociation of mass tags from the mass probes is as important as their labeling. Herein, aggregation-induced emission luminogen (AIEgen)-tagged mass probes (AIEMPs) were established to analyze estrogens, which integrated aptasensor with an explosive mass-tag signal amplification strategy via a simple ultrasound-assisted emulsification of nanoliposomes. The AIEMPs were assembled by the hybridization of aptamer-modified Fe3O4 nanoparticles (Fe NPs@Apt) and nanoliposomes loaded with massive AIEgen mass tags and partially complementary DNA strands (AIE NLs@cDNA). The aptamer was preferentially and specifically bound to estrogen, resulting in the detachment of AIE NLs from AIEMPs. Subsequently, the AIEMPs were deposited with electrospray solvents for explosive release of mass tags. Using nanoelectrospray ionization mass spectrometry (nanoESI-MS), the AIEMP-based aptasensor achieved ultrasensitive analysis of estrogens with limits of detection of 0.168-0.543 pg/mL and accuracies in the range of 87.9-114.0%. Compared to direct nanoESI-MS detection, the AIEMP-based aptasensor provides a signal amplification of four orders of magnitude. Furthermore, the utilization of different AIEMPs enables multiplexed detection of three estrogens with a miniature mass spectrometer, showing promising potential for on-site detection. This work expands the diversity of mass-tagging strategy and provides a versatile mass probe-based aptasensor platform for routine MS detection of trace analytes.

RSPSSL: A novel high-fidelity Raman spectral preprocessing scheme to enhance biomedical applications and chemical resolution visualization

Raman spectroscopy has tremendous potential for material analysis with its molecular fingerprinting capability in many branches of science and technology. It is also an emerging omics technique for metabolic profiling to shape precision medicine. However, precisely attributing vibration peaks coupled with specific environmental, instrumental, and specimen noise is problematic. Intelligent Raman spectral preprocessing to remove statistical bias noise and sample-related errors should provide a powerful tool for valuable information extraction. Here, we propose a novel Raman spectral preprocessing scheme based on self-supervised learning (RSPSSL) with high capacity and spectral fidelity. It can preprocess arbitrary Raman spectra without further training at a speed of ~1 900 spectra per second without human interference. The experimental data preprocessing trial demonstrated its excellent capacity and signal fidelity with an 88% reduction in root mean square error and a 60% reduction in infinite norm ([Formula: see text]) compared to established techniques. With this advantage, it remarkably enhanced various biomedical applications with a 400% accuracy elevation (ΔAUC) in cancer diagnosis, an average 38% (few-shot) and 242% accuracy improvement in paraquat concentration prediction, and unsealed the chemical resolution of biomedical hyperspectral images, especially in the spectral fingerprint region. It precisely preprocessed various Raman spectra from different spectroscopy devices, laboratories, and diverse applications. This scheme will enable biomedical mechanism screening with the label-free volumetric molecular imaging tool on organism and disease metabolomics profiling with a scenario of high throughput, cross-device, various analyte complexity, and diverse applications.

Single-Molecule Protein Analysis by Centrifugal Droplet Immuno-PCR with Magnetic Nanoparticles

Detecting proteins in ultralow concentrations in complex media is important for many applications but often relies on complicated techniques. Herein, a single-molecule protein analyzer with the potential for high-throughput applications is reported. Gold-coated magnetic nanoparticles with DNA-labeled antibodies were used for target recognition and separation. The immunocomplex was loaded into microdroplets generated with centrifugation. Immuno-PCR amplification of the DNA enabled the quantification of proteins at the level of single molecules. As an example, ultrasensitive detection of α-synuclein, a biomarker for neurodegenerative diseases, is achieved. The limit of detection was determined to be ∼50 aM in buffer and ∼170 aM in serum. The method exhibited high specificity and could be used to analyze post-translational modifications such as protein phosphorylation. This study will inspire wider studies on single-molecule protein detection, especially in disease diagnostics, biomarker discovery, and drug development.

Update value and clinical application of MUC16 (cancer antigen 125)

INTRODUCTION

The largest transmembrane mucin, mucin 16 (MUC16), contains abundant glycosylation sites on the molecular surface, allowing it to participate in various molecular pathways. When cells lose polarity and become cancerous, MUC16 is overexpressed, and more of the extracellular region (cancer antigen [CA]125) is released into serum and possibly, promote the development of diseases. Thus, MUC16 plays an indispensable role in clinical research and application.

AREAS COVERED

This review summarizes the update proposed role of MUC16 in carcinogenesis and metastasis. Most importantly, we prospect its potential value in targeted therapy after screening 1226 articles published within the last 10 years from PubMed. Two reviewers screened each record and each report retrieved independently. We have summarized the progress of MUC16/CA125 in basic research and clinical application, and predicted its possible future development directions.

EXPERT OPINION

As an important noninvasive co-factor in the diagnosis of gynecological diseases, MUC16 has been used for a long time, especially in the diagnosis and treatment of ovarian cancer. The overexpression of MUC16 plays a very obvious role in regulating inflammatory response, supporting immune suppression, and promoting the proliferation, division, and metastasis of cancer cells. In the next 20 years, there will be a luxuriant clinical application of MUC16 as a target for immune monitoring and immunotherapy.

DNA tetrahedron-based CRISPR bioassay for treble-self-amplified and multiplex HPV-DNA detection with elemental tagging

Sensitive quantification of multiple analytes of interest is of great significance for clinical diagnosis. CRISPR Cas platforms offer a strategy for improving the specificity, sensitivity, and speed of nucleic acid-based diagnostics, while their multiplex analysis capability is still limited and challenging. Herein, we develop a novel DNA Tetrahedron (DTN)-supported biosensor based on the spatially separated CRISPR Cas self-amplification strategy and multiple-metal-nanoparticle tagging coupled with inductively coupled plasma mass spectrometry (ICP-MS) detection to improve the sensitivity and feasibility of the platform for multiplex detection of HPV-DNA (HPV-16, HPV-18 and HPV-52). Given target DNA induces robust trans-cleavage activity of the Cas12a/crRNA duplex, and the surrounding corresponding single-stranded DNA (ssDNA) linker are cleaved into short fragments that are unable to bond metal-nanoparticle probes (¹⁹⁷Au, ¹⁰⁷Ag, ¹⁹⁵Pt) onto DTN modified magnetic beads probe (MBs-DTN), resulting in obvious ICP-MS signal change. Of note, compared with ssDNA functionalized MBs, a higher Signal-to-Noise Ratio was obtained by using MBs-DTN in our system, further amplifying the signal by regulating probes on the surface of MBs. As expected, the HPV-DNA could be detected with detection limits as low as 218 fM and be multiplexed assayed at one test with high accuracy and specificity by this proposed strategy. Furthermore, we demonstrated that the HPV-DNA in cervical swab samples could be detected, showing high consistency with DNA sequencing results. We believe that this work provides a promising option in designing CRISPR based multiplex detection system for high sensitivity, good specificity, and clinical molecular diagnostics.

Homogeneous Electrochemical Immunoassay Using an Aggregation-Collision Strategy for Alpha-Fetoprotein Detection

Homogeneous immunoassays represent an attractive alternative to traditional heterogeneous assays due to their simplicity and high efficiency. Homogeneous electrochemical assays, however, are not commonly accessed due to the requirement of electrode immobilization of the recognition elements. Herein, we demonstrate a new homogeneous electrochemical immunoassay based on the aggregation-collision strategy for the quantification of tumor protein biomarker alpha-fetoprotein (AFP). The detection principle relies on the aggregation of AgNPs induced by the molecular biorecognition between AFP and AgNPs-anti-AFP probes, which leads to an increased AgNP size and decreased AgNP concentration, allowing an accurate self-validated dual-mode immunoassay by performing nanoimpact electrochemistry (NIE) of the oxidation of AgNPs. The intrinsic one-by-one analytical capability of NIE as well as the participation of all of the atoms of the AgNPs in signal transduction greatly elevates the detection sensitivity. Accordingly, the current sensor enables a limit of detection (LOD) of 5 pg/mL for AFP analysis with high specificity and efficiency. More importantly, reliable detection of AFP in diluted human sera of hepatocellular carcinoma (HCC) patients is successfully achieved, indicating that the NIE-based homogeneous immunoassay shows great potential in HCC liquid biopsy.

DNA Tetrahedron-Based Valency Controlled Signal Probes for Tunable Protein Detection

Combined detection of multiple markers related to the same disease could improve the accuracy of disease diagnosis. However, the abundance levels of multiple markers of the same disease varied widely in real samples, making it difficult for the traditional detection method to meet the requirements of a wide detection range. Herein, three kinds of cardiac biomarkers, cardiac troponin I (cTnI), myoglobin (Myo), and C-reaction protein (CRP), which were from the pM level to the μM level in real samples, were selected as model targets. Valency-controlled signal probes based on DNA tetrahedron nanostructures (DTNs) and platinum nanoparticles (PtNPs) were constructed for tunable cardiac biomarker detection. PtNPs with high horseradish peroxidase-like activity and stability served as signal molecules, and DTNs with unique spatial structure and sequence specificity were used for precisely controlling the number of connected PtNPs. By controlling the number of PtNPs connected to DTNs, monovalent, bivalent, and trivalent signal probes were obtained and were used for the detection of cardiac markers in different concentration ranges. The limit of detection of cTnI, Myo, and CRP was 3.0 pM, 0.4 nM, and 6.7 nM, respectively. Furthermore, it performed satisfactorily for the detection of cardiac markers in 10% human serum. It was anticipated that the design of valency-controlled signal probes based on DTNs and nanozymes could be extended to the construction of other multi-target detection platforms, thus providing a basis for the development of a new precision medical detection platform.

Ultrasensitive detection of multiple cancer biomarkers by a triple cascade amplification strategy in combination with single particle inductively coupled plasma mass spectrometry

A versatile triple cascade amplification strategy was developed for ultrasensitive simultaneous detection of multiple cancer biomarkers using single particle inductively coupled plasma mass spectrometry (spICP-MS). The triple cascade amplification strategy consisted of an enhanced RecJ_f exonuclease-assisted target recycling amplification module, a hybridization chain reaction amplification module, and a signal amplification module based on DNA-templated multiple metal nanoclusters. In the enhanced RecJ_f exonuclease-assisted target recycling amplification module, the DNA bases at the 5' ends of aptamers for specific recognition of biomarkers were deliberately replaced by the corresponding RNA bases to enhance amplification efficiency. The signal amplification module based on DNA-templated multiple metal nanoclusters was innovatively used to amplify the signals measured by spICP-MS and at the same time effectively suppress possible background interferences. The proposed spICP-MS platform achieved satisfactory quantitative results for both carcinoembryonic antigen (CEA) and a-fetoprotein (AFP) in human serum samples with accuracy comparable to that of the commercial ELISA kits. Moreover, it has wide dynamic ranges for both CEA (0.01-100 ng/mL) and AFP (0.01-200 ng/mL). The limit of detection for CEA and AFP was 0.6 and 0.5 pg/mL, respectively. Compared with conventional biomarkers detection methods, the proposed spICP-MS platform has the advantages of operational simplicity, ultra-high sensitivity, wide dynamic range, and low background. Therefore, it is reasonable to expect that the proposed spICP-MS platform can be further developed to be a promising alternative tool for biomarker detection in fields of clinical diagnosis and biomedical research.

Single-Nanoparticle Differential Immunoassay for Multiplexed Gastric Cancer Biomarker Monitoring

Precision medicine demands the best application of multiple unambiguous biomarkers to bring uniform decisions in disease prognosis. The remarkable development of heterogeneous immunoassay greatly promotes precision medicine when combined with the biomarker combination strategy. Nevertheless, the cumbersome washing steps in heterogeneous immunoassay have inevitably compromised the accuracy because of the sample losses and nature change of the matrix, challenging the further exploration of a more facile and lower limit-of-detection analysis. The new methodologies with high throughputs and specificity are never out of date to provide simultaneous evaluations and uniform decisions on multiple analytes through a simple process. Herein, we propose a new wash-free immunoassay, named differential assay, for multiplexed biomarker monitoring. The method is based on counting the number difference of unbound nanoparticle tags before and after immunoreactions from a solid support (i.e., magnetic microsphere) by single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS), discarding the tedious washing steps. We primarily explore the proof-of-concept proposal within two types (sandwich and competitive assay), demonstrating the good feasibility for further facile clinical practice. To provide efficient multiplexed evaluations, we synthesized PtNPs with four diameters and screened the most suitable size for efficient differential immunoassay. The wash-free strategy was successfully utilized in simultaneous serological biomarker (CA724, CA199, and CEA) evaluation, with results in good accordance with those measured by the clinical routine method. Potentially, the proposed differential bioassay can be regarded as a more facile and valuable tool in malignancy prognosis and cancer recurrence monitoring.

Facets of ICP-MS and their potential in the medical sciences—Part 2: nanomedicine, immunochemistry, mass cytometry, and bioassays

Inductively coupled–plasma mass spectrometry (ICP-MS) has transformed our knowledge on the role of trace and major elements in biology and has emerged as the most versatile technique in elemental mass spectrometry. The scope of ICP-MS has dramatically changed since its inception, and nowadays, it is a mature platform technology that is compatible with chromatographic and laser ablation (LA) systems. Over the last decades, it kept pace with various technological advances and was inspired by interdisciplinary approaches which endorsed new areas of applications. While the first part of this review was dedicated to fundamentals in ICP-MS, its hyphenated techniques and the application in biomonitoring, isotope ratio analysis, elemental speciation analysis, and elemental bioimaging, this second part will introduce relatively current directions in ICP-MS and their potential to provide novel perspectives in the medical sciences. In this context, current directions for the characterisation of novel nanomaterials which are considered for biomedical applications like drug delivery and imaging platforms will be discussed while considering different facets of ICP-MS including single event analysis and dedicated hyphenated techniques. Subsequently, immunochemistry techniques will be reviewed in their capability to expand the scope of ICP-MS enabling analysis of a large range of biomolecules alongside elements. These methods inspired mass cytometry and imaging mass cytometry and have the potential to transform diagnostics and treatment by offering new paradigms for personalised medicine. Finally, the interlacing of immunochemistry methods, single event analysis, and functional nanomaterials has opened new horizons to design novel bioassays which promise potential as assets for clinical applications and larger screening programs and will be discussed in their capabilities to detect low-level proteins and nucleic acids.

One-step homogeneous micro-orifice resistance immunoassay for detection of chlorpyrifos in orange samples

In this work, a one-step homogeneous micro-orifice resistance immunoassay has been proposed for chlorpyrifos detection by integrating functionalized polystyrene (PS) microsphere probes with particle counting technology. The particle counter is highly sensitive and accurate for detecting the state of PS microspheres, where the particles of different states exhibit significant differences in resistance. The state of the functionalized PS microspheres is altered from dispersed to aggregated during the antigen-antibody recognition. Based on the degree of aggregation of the functionalized PS microsphere probes, chlorpyrifos can be quantitatively detected through the competitive immune response between PS antibodies and PS complete antigens. This one-step homogeneous micro-orifice resistance immunoassay simplified the procedures and greatly increased the sensitivity of detection, which has been successfully applied to detect chlorpyrifos in orange samples within 0.5 h, with the detection limit of 0.058 ng/mL.

Single Particle Inductively Coupled Plasma Mass Spectrometry-Based Homogeneous Detection of HBV DNA with Rolling Circle Amplification-Induced Gold Nanoparticle Agglomeration

A highly sensitive and simple method based on rolling circle amplification (RCA) and single particle inductively coupled plasma mass spectrometry (spICP-MS) was proposed for the homogeneous detection of hepatitis B virus (HBV) deoxyribonucleic acid (DNA). In the presence of target DNA, long ssDNA possessing a large number of repeating sequence units was generated by RCA. DNA-labeled AuNP probes assembled into long chains based on complementary base pairing, further aggregating into large particles. Small Au NPs hardly produced pulse signals in spICP-MS; obvious pulse signals appeared in spICP-MS after the agglomeration of Au NPs caused by the addition of RCA products and spermidine. On the basis of this, the homogeneous detection of target DNA was realized by spICP-MS with high sensitivity. Under optimal conditions, the proposed method exhibited a good linear relationship between the frequency of the pulse signal of Au in spICP-MS and the concentration of target HBV DNA in the range of 10-2000 fmol L^-1 (R = 0.997), the limit of detection was 5.1 fmol L^-1, and the relative standard deviation was 3.7-6.8%. Recoveries of 94.2-108% were obtained for target DNA in spiked serum samples, demonstrating a good matrix tolerance ability for the method.

Technologies for Frugal and Sensitive Point-of-Care Immunoassays

Immunoassays are a powerful tool for sensitive and quantitative analysis of a wide range of biomolecular analytes in the clinic and in research laboratories. However, enzyme-linked immunosorbent assay (ELISA)-the gold-standard assay-requires significant user intervention, time, and clinical resources, making its deployment at the point-of-care (POC) impractical. Researchers have made great strides toward democratizing access to clinical quality immunoassays at the POC and at an affordable price. In this review, we first summarize the commercially available options that offer high performance, albeit at high cost. Next, we describe strategies for the development of frugal POC assays that repurpose consumer electronics and smartphones for the quantitative detection of analytes. Finally, we discuss innovative assay formats that enable highly sensitive analysis in the field with simple instrumentation.

Standard-free single magnetic bead evaluation: a stable nanoplatform for prostate disease differentiation

Explicit interpretation of heterogeneity between prostate-specific antigen (PSA) subtypes is essential for prostate cancer differentiation during different disease courses, whereas a universal protocol with uniform criteria is still lacking across the globe. In this work, a standard-free single magnetic bead (SMB) nanoplatform utilizing metal nanoparticles with optimal diameters was proposed for prostate disease differentiation in a 134-donor model. The inaccuracy of detection in absolute quantification was diminished via evaluations of metal intensities on the single magnetic bead. The intrinsic proportion of fPSA in tPSA was successfully evaluated by direct use of the Pt to Au intensity ratio (Pt/Au ratio), exhibiting better differentiation between healthy and unhealthy, benign prostatic hyperplasia (BPH) and cancer individuals compared with solo fPSA or tPSA. We generated thresholds respectively for prostate disease differentiation, envisioning that this standard-free SMB nanoplatform would establish a standardized methodology with uniform criteria worldwide in cancer diagnosis, staging, and postoperative assessments.

Serum Nardilysin as a Prognostic Biomarker in Pancreatic Ductal Adenocarcinoma

Background: Nardilysin, (N-arginine dibasic convertase, NRDC) has been reported to play an important role in cancer progression, and is associated with tumor proliferation signals and inflammatory signals, such as tumor necrosis factor-a (TNF-a) and heparin-binding epidermal growth factor-like growth factor (HB-EGF), through the activation of disintegrin and metalloproteinase (ADAM) proteases. NRDC has recently been revealed to be involved in the tumorigenesis of various types of cancer, including intrahepatic cholangiocarcinoma, malignant cerebral infarction, esophageal squamous cell carcinoma, and gastric cancer. However, the expression profiles and biological relevance of NRDC in pancreatic ductal adenocarcinoma have rarely been reported. Methods: We analyzed the NRDC expression profile in pancreatic ductal adenocarcinoma by enzyme-linked immunosorbent assay (ELISA) and identified NRDC as a circulating biomarker in the serum of 112 pancreatic ductal adenocarcinoma patients. The diagnostic value of NRDC was analyzed by the area under the curve (AUC) and the receiver operating characteristic (ROC) test. Results: Our results demonstrated that the clinical prognosis significance of NRDC with the clinical characteristics in pancreatic ductal adenocarcinoma (PDAC). NRDC was notably decreased in PDAC patient serum compared with the control group (p < 0.001). Furthermore, the present study found that the NRDC expression level was correlated with T grade (p < 0.001), metastasis(p < 0.001), differentiation(p < 0.001), and TNM stage (p = 0.011). Further bioinformatics analysis revealed that NRDC correlated with proliferation and migration pathways; in particular, it mediated cell-matrix adhesion-dependent activation in pancreatic ductal adenocarcinoma. Conclusions: Serum NRDC may play a useful diagnostic biomarker to evaluate the aggressive clinical features in PAAD patients.

Review about Powerful Combinations of Advanced and Hyphenated Sample Introduction Techniques with Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for Elucidating Trace Element Species in Pathologic Conditions on a Molecular Level

Element analysis in clinical or biological samples is important due to the essential role in clinical diagnostics, drug development, and drug-effect monitoring. Particularly, the specific forms of element binding, actual redox state, or their spatial distribution in tissue or in single cells are of interest in medical research. This review summarized exciting combinations of sophisticated sample delivery systems hyphenated to inductively coupled plasma-mass spectrometry (ICP-MS), enabling a broadening of information beyond the well-established outstanding detection capability. Deeper insights into pathological disease processes or intracellular distribution of active substances were provided, enabling a better understanding of biological processes and their dynamics. Examples were presented from spatial elemental mapping in tissue, cells, or spheroids, also considering elemental tagging. The use of natural or artificial tags for drug monitoring was shown. In the context of oxidative stress and ferroptosis iron, redox speciation gained importance. Quantification methods for Fe2+, Fe3+, and ferritin-bound iron were introduced. In Wilson’s disease, free and exchangeable copper play decisive roles; the respective paragraph provided information about hyphenated Cu speciation techniques, which provide their fast and reliable quantification. Finally, single cell ICP-MS provides highly valuable information on cell-to-cell variance, insights into uptake of metal-containing drugs, and their accumulation and release on the single-cell level.

A double reaction system induced electrochemiluminescence enhancement based on SnS2 QDs@MIL-101 for ultrasensitive detection of CA242

At present, the development of electrochemiluminescence (ECL) immunosensor with excellent performance is still the research focus of immunoassay and detection. Herein, SnS₂ quantum dots (SnS₂ QDs) and metal-organic framework (MIL-101 (Cr)) are effectively combined to achieve synergistic signal amplification based on K₂S₂O₈ co-reactant, thereby constructing SnS₂ QDs/SO₄^•- and SO₄^•-/O₂ ECL double reaction luminous systems. SnS₂ QDs and singlet oxygen (¹(O₂)₂*) produced from the system as light-emitting devices jointly enhance the ECL response and significantly improve the sensitivity of the ECL immunosensor. Dissolved oxygen and SnS₂ QDs respectively generate HOO^• and SnS₂ QDs^•- under negative potential, and react with transient SO₄^•- to emit strong light respectively, so as to jointly enhance the ECL response. MIL-101 catalyzes the oxygen cathode reduction reaction to promote the conversion of dissolved oxygen into HOO^•, which greatly improves the ECL response of ¹(O₂)₂*. CuS with spherical nanoflower-like form as a co-reaction promoter of K₂S₂O₈ generate more SO₄^•- active substances, which further enhance the ECL response of the immunosensor. The constructed ECL immunosensor has the advantages of low detection limit, high sensitivity and better stability. Under the optimal conditions, the detection range is 0.1 mU/mL∼100 U/mL, and the detection limit is 0.015 mU/mL. The results show that the constructed ECL immunosensor can detect human CA242 samples and have a broad application prospect in biological analysis and early diagnosis of diseases.

Highly sensitive and multiplexed mass spectrometric immunoassay techniques and clinical applications

Immunoassay is one of the most important clinical techniques for disease/pathological diagnosis. Mass spectrometry (MS) has been a popular and powerful readout technique for immunoassays, generating the mass spectrometric immunoassays (MSIAs) with unbeatable channels for multiplexed detection. The sensitivity of MSIAs has been greatly improved with the development of mass labels from element labels to small-molecular labels. MSIAs are also expended from the representative element MS-based methods to the laser-based organic MS and latest ambient MS, improving in both technology and methodology. Various MSIAs present high potential for clinical applications, including the biomarker screening, the immunohistochemistry, and the advanced single-cell analysis. Here, we give an overall review of the development of MSIAs in recent years, highlighting the latest improvement of mass labels and MS techniques for clinical immunoassays.

A homogeneous nucleic acid assay for simultaneous detection of SARS-CoV-2 and influenza A (H3N2) by single-particle inductively coupled plasma mass spectrometry

In recent years, single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) has become a powerful tool for biological quantitative analysis. Homogeneous analysis method requires no separation and washing steps, which is suited for the analysis of highly infectious pathogens, so as to reduce the risk of infection during the operation. SARS-CoV-2 spreads all over the world, and its early infection symptoms are similar to influenza, which brings inconvenience to triage. Therefore, developing novel analytical method for simultaneous detection of multiple viral nucleic acids is essential. Taking the advantages of SP-ICP-MS and homogeneous analysis strategy, a SP-ICP-MS homogeneous nucleic acid assay by using gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs) probes was established for simultaneous sensitive analysis of SARS-CoV-2 and influenza A (H3N2). In the present of target SARS-CoV-2 or H3N2 nucleic acids, corresponding Au NPs or Ag NPs probes form larger aggregates, resulting in increased pulse signal intensity and reduced pulse signal frequency of the corresponding NPs in SP-ICP-MS measurement. In this assay, the reaction system of Au NPs and Ag NPs probes does not interfere with each other, and there was no separation and washing procedure, which facilitates operation, saves the analysis time, and improves the analysis efficiency. The linear range of this method is 5-1000 pmol L^-1, with low-level limits of quantification of target nucleic acid. The developed SP-ICP-MS simultaneous homogeneous detection method has a good potential for detecting nucleic acid, protein, cell and other biological samples by changing different modification sequences on the NPs probes.

Lanthanide Nanoprobes for the Multiplex Evaluation of Breast Cancer Biomarkers

Metal stable isotope tagging has demonstrated great and unique success in the multiplex and ratiometry-based accurate detection of biomolecules and single cells, while its sensitivity is regarded as an Achilles' heel. Although lanthanide nanoparticles remain the most promising tags for elemental mass spectrometry, there is no report on the lanthanide nanoparticle-based multiplex immunoassay of disease markers in clinical serum samples because of their tough synthesis and bioconjugation and a complex physiological sample matrix. Herein, to fill this gap, multiple lanthanide nanoparticle tags (NaEuF₄, NaTbF₄, and NaHoF₄) were delicately designed and facilely synthesized with a one-pot solvothermal method for the multiplex evaluation of breast cancer biomarkers carcinoembryonic antigen (CEA), CA153, and CA125 in human serum samples. The proposed method exhibited wide linear ranges and low levels of the detection limit for all biomarkers. The test results were consistent with the routine electrochemiluminescence results in clinical serum samples, which proved the possibility of the early prognosis of breast cancer as well as improving the surgical outcome prediction.

Quantification of Tumor Protein Biomarkers from Lung Patient Serum Using Nanoimpact Electrochemistry

Protein quantification with high throughput and high sensitivity is essential in the early diagnosis and elucidation of molecular mechanisms for many diseases. Conventional approaches for protein assay often suffer from high costs, long analysis time, and insufficient sensitivity. The recently emerged nanoimpact electrochemistry (NIE), as a contrast, allows in situ detection of analytes one at a time with simplicity, fast response, high throughput, and the potential of reducing the detection limits down to the single entity level. Herein, we propose a NIE-enabled electrochemical immunoassay using silver nanoparticles (AgNPs) as labels for the detection of CYFRA21-1, a typical protein marker for lung carcinoma. This strategy is based on the measurement of the impact frequency and the charge intensity of the electrochemical oxidation of individual AgNPs before and after they are modified with anti-CYFRA21-1 and in turn immunocomplexed with CYFRA21-1. Both the frequency and intensity modes of single-nanoparticle electrochemistry correlate well with each other, resulting in a self-validated immunoassay that provides linear ranges of two orders of magnitude and a limit of detection of 0.1 ng/mL for CYFRA21-1 analysis. The proposed immunoassay also exhibits excellent specificity when challenged with other possible interfering proteins. In addition, the CYFRA21-1 content is validated by a conventional, well-known enzyme-linked immunosorbent assay and successfully quantified in a diluted healthy serum with a satisfactory recovery. Moreover, CYFRA21-1 detection in serum samples of lung cancer patients is successfully demonstrated, suggesting the feasibility of the NIE-based immunoassay in clinically relevant diagnosis. To the best of our knowledge, this is the first report to construct NIE-based electrochemical immunoassays for the specific detection of tumor protein biomarkers.

Single-Nanoparticle ICP-MS for Sensitive Detection of Uracil-DNA Glycosylase Activity

Single-nanoparticle inductively coupled plasma mass spectrometry (SP-ICP-MS) has demonstrated unique advantages for the detection of biological samples. However, methods for enzyme activity detection based on SP-ICP-MS technology have been rarely explored. Here we report the development of a novel SP-ICP-MS assay for uracil-DNA glycosylase (UDG) activity detection based on its ability to specifically recognize and remove uracil to induce the cleavage of the DNA probe. Our design allows the generation of single gold nanoparticles correlated to the specific enzymatic reaction for a highly sensitive SP-ICP-MS measurement. The developed assay enables sensitive UDG activity detection with a detection limit of 0.0003 U/mL. The cell lysate analysis by the developed assay reveals its applicability for the detection of UDG activity in real samples. It is envisioned that our design may provide a new paradigm for developing the SP-ICP-MS assay for enzyme activity detection in biological samples.

A Homogeneous Multicomponent Nucleic Acid Enzyme Assay for Universal Nucleic Acid Detection by Single-Particle Inductively Coupled Plasma Mass Spectrometry

Single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) has great potential for sensitive analysis of nucleic acids; however, it usually requires separation of target-induced nanoparticle reporters, and the sequence of probes on nanoparticle reporters has to be tuned for each target accordingly. Here, we developed a homogeneous multicomponent nucleic acid enzyme (MNAzyme) assay for universal nucleic acid detection. The two components of MNAzyme contain target recognition sites, substrate binding sites, and a catalytic core. Only in the presence of a specific nucleic acid target, the MNAzyme will assemble to trigger its nucleic acid enzyme activity and cleave its substrate (Linker DNA). The Linker DNA could link gold nanoparticle (AuNP) probes to form a larger assembled particle, while the cleavage of Linker DNA will disturb the linkage between probes, inducing a smaller assembled particle. The assembled particles with different sizes could be differentiated and sensitively detected in SP-ICP-MS, which also enables the tolerance of a complex matrix. By simply altering the sequences of the target recognition sites in MNAzyme, we applied the assay for two types of nucleic acids (long strand DNA and short strand RNA), malaria DNA and miRNA-10b. With increasing the target concentration, the signal intensity of each assembled particle decreases, but the frequency of assembled particle pulse increases. Both targets could be quantitatively detected from 0.1 to 25 pmol L^-1 with high specificity in serum samples. The developed MNAzyme-SP-ICP-MS assay possesses simple operation in a homogeneous reaction, easy tunability for multiple types of nucleic acid targets, and good compatibility with clinic samples.