Nanoparticles as labels of specific-recognition reactions for the determination of biomolecules by inductively coupled plasma-mass spectrometry

Pathogen detection via inductively coupled plasma mass spectrometry analysis with nanoparticles

Infections caused by viruses and bacteria pose a significant threat to global public health, emphasizing the critical importance of timely and precise detection methods. Inductively coupled plasma mass spectrometry (ICP-MS), a contemporary approach for pathogen detection, offers distinct advantages such as high sensitivity, a wide linear range, and multi-index capabilities. This review elucidates the underexplored application of ICP-MS in conjunction with functional nanoparticles (NPs) for the identification of viruses and bacteria. The review commences with an elucidation of the underlying principles, procedures, target pathogens, and NP requirements for this innovative approach. Subsequently, a thorough analysis of the advantages and limitations associated with these techniques is provided. Furthermore, the review delves into a comprehensive examination of the challenges encountered when utilizing NPs and ICP-MS for pathogen detection, culminating in a forward-looking assessment of the potential pathways for advancement in this domain. Thus, this review contributes novel perspectives to the field of pathogen detection in biomedicine by showcasing the promising synergy of ICP-MS and NPs.

Advancing SERS as a quantitative technique: challenges, considerations, and correlative approaches to aid validation

Surface-enhanced Raman scattering (SERS) remains a significant area of research since it's discovery 50 years ago. The surface-based technique has been used in a wide variety of fields, most prominently in chemical detection, cellular imaging and medical diagnostics, offering high sensitivity and specificity when probing and quantifying a chosen analyte or monitoring nanoparticle uptake and accumulation. However, despite its promise, SERS is mostly confined to academic laboratories and is not recognised as a gold standard analytical technique. This is due to the variations that are observed in SERS measurements, mainly caused by poorly characterised SERS substrates, lack of universal calibration methods and uncorrelated results. To convince the wider scientific community that SERS should be a routinely used analytical technique, the field is now focusing on methods that will increase the reproducibility of the SERS signals and how to validate the results with more well-established techniques. This review explores the difficulties experienced by SERS users, the methods adopted to reduce variation and suggestions of best practices and strategies that should be adopted if one is to achieve absolute quantification.

Unveiling compositional images of specific proteins in individual cells by LA-ICP-MS: Labelling with ruthenium red and metal nanoclusters

BACKGROUND

Recent biological studies have demonstrated that changes can occur in the cellular genome and proteome due to variations in cell volume. Therefore, it is imperative to take cell volume into account when analyzing a target protein. This consideration becomes especially critical in experimental models involving cells subjected to different treatments. Failure to consider cell volume could obscure the studied biological phenomena or lead to erroneous conclusions. However, quantitative imaging of proteins within cells by LA-ICP-MS is limited by the lack of methods that provide the protein concentration (protein mass over cell volume) rather than just protein mass within individual cells.

RESULTS

The combination of a metal tagged immunoprobe with ruthenium red (RR) labelling enables the simultaneous analysis of a specific protein and the cell volume in each cell analyzed by LA-ICP-(Q)MS. The results indicate that the CYP1B1 concentration exhibits a quasi-normally distribution in control ARPE-19 cells, whereas AAPH-treated cells reveal the presence of two distinct cell groups, responding and non-responding cells to an in vitro induced oxidative stress. The labelling of the membrane with RR and the measurement of Ru mass in each cell by LA-ICP-MS offers higher precision compared to manually delimitation of the cell perimeter and eliminates the risk of biased information, which can be prone to inter-observer variability. The proposed procedure is fast and minimizes errors in cell area assignment and offers the possibility to carry out a faster data treatment approach if just relative volumes are compared, which can be advantageous for specific applications.

SIGNIFICANCE AND NOVELTY

This work presents an innovative strategy to directly study the distribution and concentration of proteins within individual cells by LA-ICP-MS. This method employs ruthenium red as a cell volume marker and Au nanoclusters (AuNCs) tagged immunoprobes to label the protein of interest. Furthermore, the proposed labelling strategy enables rapid data processing, allowing for the calculation of relative concentrations and thus facilitating the comparison across large datasets. As a proof-of-concept, the concentration of the CYP1B1 protein was quantified in ARPE-19 cells under both control and oxidative stress conditions.

Detection of terminal deoxynucleotidyl transferase activity based on self-mediated nucleic acid elongation and elemental labeling inductively coupled plasma-mass spectrometry

Terminal deoxynucleotidyl transferase (TdT), a specialized DNA polymerase, is recognized as a promising biomarker for acute leukemia. Herein, taking the advantage of the self-mediated strand elongation property of TdT, a simple and sensitive method for TdT activity assay was developed based on gold nanoparticles (AuNPs) labeling inductively coupled plasma mass spectrometry (ICP-MS). In the presence of TdT, the primer DNA on magnetic beads is elongated with an adenine-rich single stranded long chain that can label poly-thymine modified AuNPs. After acid elution, the labeled AuNPs were detected by ICP-MS, and the signal intensity of 197Au reflected the TdT activity. Under the optimal conditions, the limit of detection for TdT activity is down to 0.054 U mL-1, along with good selectivity and strong tolerance to other interfering proteins. Furthermore, it achieves a straightforward and accurate detection of TdT activity in acute lymphoblastic leukemia cells without sample pre-processing and tool enzyme addition. Therefore, the proposed method shows great promise as a valuable tool for TdT-related biological research and leukemia therapeutics.

Simultaneous determination of inflammatory factors SAA and LTF based on stable element labeling and inductively coupled plasma mass spectrometry to aid in the diagnosis of infection

OBJECTIVE

The clinical value of Serum amyloid A (SAA) and Lactoferrin (LTF) has received significant attention, but their detection methods are inadequate, which limits their application. This study aims to develop a dual detection method based on stable element labeling strategies and inductively coupled plasma mass spectrometry (ICP-MS) for SAA/LTF and to assess whether it can be widely used in clinical practice.

METHODS

A duplex immunoassay system based on sandwich method was constructed. After optimization, methodological evaluation was performed with the guidelines of Clinical Laboratory Standards Institute (CLSI). Finally, 131 plasma samples were collected to analyze whether the new method is suitable for clinical detection.

RESULTS

The LoB, LLoQ, ULoQ, and linear range of the assay were 1.09 ng/mL, 3 ng/mL, 1500 ng/mL, 3-1500 ng/mL for SAA and 0.85 ng/mL, 2 ng/mL, 1200 ng/mL, 2-1200 ng/mL for LTF respectively. The recovery rates were 95.01% to 106.26%, the intra-batch precision of low, intermediate, and high-level samples was <8%, and the inter-batch of them was <11%, the deviation of interference test results was less than±10%. The Area Under the Curve (AUC) was 0.9809 for SAA, 0.8599 for LTF, and 0.9986 for combination.

CONCLUSION

The quantitative duplex immunoassay for SAA/LTF has high accuracy, good precision, and high specificity, which meets the clinical testing requirements and can be widely used in clinical practice.

Palladium nanoclusters as a label to determine GFAP in human serum from donors with stroke by bimodal detection: inductively coupled plasma-mass spectrometry and linear sweep voltammetry

Water-soluble, stable, and monodisperse palladium nanoclusters (PdNCs) were synthesized using NaBH4 as a reductant and lipoic acid as a ligand. PdNCs, measured by high-resolution transmission electron microscopy, showed a round shape and a diameter of 2.49 ± 0.02 nm. It was found that each PdNC contains 550 Pd atoms on average. These PdNCs offer high amplification as a label of biochemical reactions when inductively coupled plasma-mass spectrometry (ICP-MS) is used as a detector. In addition, PdNCs have catalytic activity on electrochemical reactions, allowing detection by linear sweep voltammetry (LSV). As a proof of applicability, a competitive immunoassay based on PdNC labels was developed for the determination of glial fibrillary acidic protein (GFAP) in human serum, comparing ICP-MS and LSV detection. GFAP is a biomarker for differentiating between patients with ischemic stroke (IS) and hemorrhagic stroke (HS). The limit of detection (LoD), corresponding to IC10 (4-parameter logistic curve), was 0.03 pM of GFAP, both by ICP-MS and LSV, being lower than the 0.31 pM LoD provided by the ELISA commercial kit. Using the error profile method, 0.03 pM and 0.11 pM LoDs were obtained respectively by ICP-MS and LSV: LoD is lower by ICP-MS due to the better precision of the measurements. The analyses of human serum samples from IS, HS, and control (CT) donors using PdNC labels and detection by ICP-MS and LSV were validated with a commercial ELISA kit (for CT donors only ICP-MS provided enough sensitivity). Results point out toward the future use of PdNCs as a label in other immunoprobes for the determination of specific proteins requiring very low LoDs as well as the development of electrochemical decentralized methodologies.

Study on the detection of anthrax by ICP-MS based on gold nanoparticle labeling

BACKGROUND

In recent years, inductively coupled plasma mass spectrometry (ICP-MS) has been widely used in the field of molecular biology because of its unique advantages. Anthrax is a widespread and long-standing infectious disease, which affects and restricts people's work and life seriously.

OBJECTIVE

The study goal is to develop a new method for the detection of anthrax.

METHODS

A rapid, sensitive and accurate method for the detection of anthrax characteristic DNA was proposed by combing gold nanoparticles (AuNPs) and inductively coupled plasma mass spectrometry.

RESULTS

The linear range of this method is 100-2500 pmol/L and the limit of detection of 16.61 pmol/L.

CONCLUSION

The proposed method has numerous advantages, including simplicity of operation, high sensitivity, and specificity, which provides a new idea for the detection of anthrax. Importantly, this methodology has good potential for the detection of other biological substances such as bacteria and viruses by changing the modification sequence on the nanoparticle probe.

Single-cell ICP-MS to address the role of trace elements at a cellular level

The heterogeneity properties shown by cells or unicellular organisms have led to the development of analytical methods at the single-cell level. In this sense, considering the importance of trace elements in these biological systems, the inductively coupled plasma mass spectrometer (ICP-MS) configured for analyzing single cell has presented a high potential to assess the evaluation of elements in cells. Moreover, advances in instrumentation, such as coupling laser ablation to the tandem configuration (ICP-MS/MS), or alternative mass analyzers (ICP-SFMS and ICP-TOFMS), brought significant benefits, including sensitivity improvement, high-resolution imaging, and the cell fingerprint. From this perspective, the single-cell ICP-MS has been widely reported in studies involving many fields, from oncology to environmental research. Hence, it has contributed to finding important results, such as elucidating nanoparticle toxicity at the cellular level and vaccine development. Therefore, in this review, the theory of single-cell ICP-MS analysis is explored, and the applications in this field are pointed out. In addition, the instrumentation advances for single-cell ICP-MS are addressed.

Infrared Laser Desorption of Intact Nanoparticles for Digital Tissue Imaging

We report a new technique for the digital mapping of biomarkers in tissues based on desorption and counting intact gold nanoparticle (Au NP) tags using infrared laser ablation single-particle inductively coupled plasma mass spectrometry (IR LA SP ICP MS). In contrast to conventional UV laser ablation, Au NPs are not disintegrated during the desorption process due to their low absorption at 2940 nm. A mass spectrometer detects up to 83% of Au NPs. The technique is demonstrated on mapping a proliferation marker, nuclear protein Ki-67, in three-dimensional (3D) aggregates of colorectal carcinoma cells, and the results are compared with confocal fluorescence microscopy and UV LA ICP MS. Precise counting of 20 nm Au NPs with a single-particle detection limit in each pixel by the new approach generates sharp distribution maps of a specific biomarker in the tissue. Advantageously, the desorption of Au NPs from regions outside the tissue is strongly suppressed. The developed methodology promises multiplex mapping of low-abundant biomarkers in numerous biological and medical applications using multielemental mass spectrometers.

Detection of Histidine-Tagged Protein in Escherichia coli by Single-Cell Inductively Coupled Plasma-Mass Spectrometry

We have developed a rapid and precise quantification method for a histidine (His)-tagged recombinant protein produced in Escherichia coli (E. coli) by single-cell inductively coupled plasma-mass spectrometry (SC-ICP-MS). Plasmid vector containing enhanced green fluorescent protein (EGFP) or red fluorescent protein (mCherry) gene fused with His-tag was transformed into E. coli. The transformed E. coli was exposed to nickel (Ni) chloride or cobalt (Co) chloride for labeling His-tag with the Ni or Co ion. Then, E. coli was analyzed by SC-ICP-MS to determine the amount of EGFP or mCherry protein on the basis of the signal of Ni or Co bound to His-tag. By comparing Ni and Co contents in E. coli expressing His-tagged mCherry with those in nontagged mCherry, the specific binding of Co to His-tag was more clearly detected than that of Ni. The Co contents were increased until 6 h after the protein induction, and this observation was coincident with the increases in fluorescence intensity of EGFP or mCherry measured by a flow cytometer. However, the Co contents were decreased for EGFP and kept at a constant level for mCherry from 6 to 24 h despite the continuous increase in the fluorescence intensity through incubation. The fluorescent proteins were mainly recovered in the insoluble fraction 24 h after the induction. This can be explained by the fact that the overexpressed fluorescent proteins with His-tag are transferred into inclusion bodies, which hampers the binding of the fluorescent proteins to the Co ion. SC-ICP-MS can be a useful technique to precisely quantify soluble recombinant proteins in E. coli without the extraction and purification process.

Living in a transient world: ICP-MS reinvented via time-resolved analysis for monitoring single events

After 40 years of development, inductively coupled plasma-mass spectrometry (ICP-MS) can hardly be considered as a novel technique anymore. ICP-MS has become the reference when it comes to multi-element bulk analysis at (ultra)trace levels, as well as to isotope ratio determination for metal(loid)s. However, over the last decade, this technique has managed to uncover an entirely new application field, providing information in a variety of contexts related to the individual analysis of single entities (e.g., nanoparticles, cells, or micro/nanoplastics), thus addressing new societal challenges. And this profound expansion of its application range becomes even more remarkable when considering that it has been made possible in an a priori simple way: by providing faster data acquisition and developing the corresponding theoretical substrate to relate the time-resolved signals thus obtained with the elemental composition of the target entities. This review presents the underlying concepts behind single event-ICP-MS, which are needed to fully understand its potential, highlighting key areas of application (e.g., single particle-ICP-MS or single cell-ICP-MS) as well as of future development (e.g., micro/nanoplastics).

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.

Mass Spectrometric Biosensing: A Powerful Approach for Multiplexed Analysis of Clinical Biomolecules

Rapid and sensitive detection of clinical biomolecules in a multiplexed fashion is of great importance for accurate diagnosis of diseases. Mass spectrometric (MS) approaches are exceptionally suitable for clinical analysis due to its high throughput, high sensitivity, and reliable qualitative and quantitative capabilities. To break through the bottleneck of MS technique for detecting high-molecular-weight substances with low ionization efficiency, the concept of mass spectrometric biosensing has been put forward by adopting mass spectrometric chips to recognize the targets and mass spectrometry to detect the signals switched by the recognition. In this review, the principle of mass spectrometric sensing, the construction of different mass tags used for biosensing, and the typical combination mode of mass spectrometric imaging (MSI) technique are summarized. Future perspectives including the design of portable matching platforms, exploitation of novel mass tags, development of effective signal amplification strategies, and standardization of MSI methodologies are proposed to promote the advancements and practical applications of mass spectrometric biosensing.

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Imaging in Biology

Elemental imaging gives insight into the fundamental chemical makeup of living organisms. Every cell on Earth is comprised of a complex and dynamic mixture of the chemical elements that define structure and function. Many disease states feature a disturbance in elemental homeostasis, and understanding how, and most importantly where, has driven the development of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) as the principal elemental imaging technique for biologists. This review provides an outline of ICP-MS technology, laser ablation cell designs, imaging workflows, and methods of quantification. Detailed examples of imaging applications including analyses of cancers, elemental uptake and accumulation, plant bioimaging, nanomaterials in the environment, and exposure science and neuroscience are presented and discussed. Recent incorporation of immunohistochemical workflows for imaging biomolecules, complementary and multimodal imaging techniques, and image processing methods is also reviewed.

Laser-induced breakdown spectroscopy as a readout method for immunocytochemistry with upconversion nanoparticles

Immunohistochemistry (IHC) and immunocytochemistry (ICC) are widely used to identify cancerous cells within tissues and cell cultures. Even though the optical microscopy evaluation is considered the gold standard, the limited range of useful labels and narrow multiplexing capabilities create an imminent need for alternative readout techniques. Laser-induced breakdown spectroscopy (LIBS) enables large-scale multi-elemental analysis of the surface of biological samples, e.g., thin section or cell pellet. It is, therefore, a potential alternative for IHC and ICC readout of various labels or tags (Tag-LIBS approach). Here, we introduce Tag-LIBS as a method for the specific determination of HER2 biomarker. The cell pellets were labeled with streptavidin-conjugated upconversion nanoparticles (UCNP) through a primary anti-HER2 antibody and a biotinylated secondary antibody. The LIBS scanning enabled detecting the characteristic elemental signature of yttrium as a principal constituent of UCNP, thus indirectly providing a reliable way to differentiate between HER2-positive BT-474 cells and HER2-negative MDA-MB-231 cells. The comparison of results with upconversion optical microscopy and luminescence intensity scanning confirmed that LIBS is a promising alternative for the IHC and ICC readout.