Highly Sensitive Immunoassay for the Diagnosis of Acute Myocardial Infarction Using Silica Spheres Encapsulating a Quantum Dot Layer

Exploring T7 RNA polymerase-assisted CRISPR/Cas13a amplification for the detection of BNP via electrochemiluminescence sensing platform

Brain natriuretic peptide (BNP) is considered to be an important biomarker of heart failure (HF) attracting attention. However, its low concentration and short half-life in blood lead to a low-sensitivity detection of BNP, which is a challenge that has to be overcome. In this work, we propose a highly specific, highly sensitive T7 RNA polymerase-assisted clustered regularly interspaced short palindromic repeats (CRISPR)/Cas13a system to detect BNP via an electrochemiluminescence (ECL) sensing platform and incorporate exonuclease III (Exo III)-hairpin and dumbbell-shaped hybridization chain reaction (HCR) technologies. In this detection scheme, the ECL sensing platform possesses low background signal and high sensitivity. Firstly, the T7 promoter-initiated T7 RNA polymerase acts as a signal amplification technique to generate large amounts of RNAs that can activate CRISPR/Cas13a activity. Secondly, CRISPR/Cas13a is able to trans-cleave the surrounding trigger strand to produce DNA1. Thirdly, DNA1 is involved in the co-amplification reaction of Exo III and hairpin DNA, which subsequently triggers a dumbbell-shaped HCR technology. Eventually, a large number of Ru (II) molecules are inserted into the interstitial space of the dumbbell-shaped HCR to generate a strong ECL signal. The CRISPR/Cas13a possesses outstanding specificity for a single base and increased sensitivity. The tightly conformed dumbbell-shaped HCR provides higher sensitivity than the traditional linear HCR amplification technique. Ultimately, the clever combination of several amplification reactions enables the limit of detection (LOD) as low as 3.2 fg/mL. It showed promise for clinical sample testing, with recovery rates ranging from 98.4% to 103% in 5% human serum samples. This detection method offered a valuable tool for early HF detection, emphasizing the synergy of amplification strategies and specificity conferred by CRISPR/Cas13a technology.

Mass spectrometric studies on the peptide integrity of substance P and related human tachykinins in human biofluids

The neurokinin-1 receptor plays a profound role in inflammatory processes and is involved in immune cell differentiation, cytokine release, and mast cell activation. Due to their similar peptide structures, the neurokinin-1 receptor does not discriminate between the endogenous ligands substance P (SP) and human hemokinin-1 (hHK-1), which both demonstrate biological receptor affinity. In addition, due to cross-reactivity, the current bioanalytical method of choice-immunoassays-also displays limitations in differentiating between these peptides. Thus, a recently developed mass spectrometric assay was utilized for the selective quantification of SP and hHK-1 in various biofluids and tissue. By applying the sample processing protocols developed, SP was quantified in porcine brain tissue (4.49 ± 0.53 nM), human saliva (113.3 ± 67.0 pM), and human seminal fluid (0.52 ± 0.15 nM) by mass spectrometric analysis. As previously reported, neither SP nor hHK-1 could be detected in human plasma by mass spectrometry. Comparison with analysis using a commercial immunoassay of the same plasma sample revealed SP like-immunoreactivity concentrations of 37.1-178.0 pM. The previously reported carboxylic acid of SP, whose identity was confirmed by high-resolution mass spectrometric analysis, did not show cross-reactivity in the applied immunoassay and did not contribute to SP-like immunoreactivity results. Subsequent compound discovery of the immunocaptured substance indicated the presence of a precursor of SP as possible cross-reactor in human plasma samples. The found cross-reactivity might be the cause for the high variance of SP plasma levels in former determinations.

Fully Self-Assembled Silica Nanoparticle-Semiconductor Quantum Dot Supra-Nanoparticles and Immunoconjugates for Enhanced Cellular Imaging by Microscopy and Smartphone Camera

There is a growing need for brighter luminescent materials to improve the detection and imaging of biomarkers. Relevant contexts include low-abundance biomarkers and technology-limited applications, where an example of the latter is the emerging use of smartphones and other nonoptimal but low-cost and portable devices for point-of-care diagnostics. One approach to achieving brighter luminescent materials is incorporating multiple copies of a luminescent material into a larger supra-nanoparticle (supra-NP) assembly. Here, we present a facile method for the preparation and immunoconjugation of supra-NP assemblies (SiO₂@QDs) that comprised many quantum dots (QDs) around a central silica nanoparticle (SiO₂ NP). The assembly was entirely driven by spontaneous affinity interactions between the constituent materials, which included imidazoline-functionalized silica nanoparticles, ligand-coated QDs, imidazole-functionalized dextran, and tetrameric antibody complexes (TACs). The physical and optical properties of the SiO₂@QDs were characterized at both the ensemble and single-particle levels. Notably, the optical properties of the QDs were preserved upon assembly into supra-NPs, and single SiO₂@QDs were approximately an order of magnitude brighter than single QDs and nonblinking. In proof-of-concept applications, including selective immunolabeling of breast cancer cells, the SiO₂@QDs provided higher sensitivity and superior signal-to-background ratios whether using research-grade fluorescence microscopy or smartphone-based imaging. Overall, the SiO₂@QDs are promising materials for enhanced bioanalysis and imaging.

Electrochemiluminescent biosensor with DNA link for selective detection of human IgG based on steric hindrance

A highly selective DNA-based electrochemiluminescence (ECL) based biosensor is described for the detection of human IgG. It is exploiting the effect of steric hindrance that affects the strength of the ECL signal in the presence of IgG. Digoxin-linked signaling DNA was specifically bound to IgG, and this causes steric hindrance which limits the ability of DNA to hybridize with capturing DNA attached to a gold electrode. Europium (II) doped CdSe quantum dots were covalently linked to the DNA in order to generate the ECL signal. Using this steric hindrance hybridization method, the ECL signal of the biosensor were proportional to the concentration of IgG with a wide linear range and a 14 pM detection limit. Conceivably, the method can be expanded to the detection of a wide range of proteins for which homologous recognition elements are available.

Direct Hybridization of Hydrophobic Nanocrystals with Colloidal Silica via van der Waals Force

We present a novel, direct approach to hybridize hydrophobic quantum dot (QD) nanocrystals with colloidal silica (A) via van der Waals (vdW) force only. The A is constructed by aggregation of 15-25 nm sized hydrophobic silica nanoparticles with octadecyl groups. For hybridization, the hydrophobic QDs sit on the crevices of A via reinforced vdW force by interdigitation of long-chained hydrocarbons along the enlarged contact area of the crevices. The hybrids (B) are easily encapsulated with silica with/without functional groups, yielding QD-layer-incorporated silica particles (C) with greatly enhanced PL (up to 690%) and astonishing photostability compared with their free QDs under an identical QD concentration. This approach is simple, novel, versatile, and extended to the cases of three different sized QDs. The hydrophobic product C with phenylethyl groups is applicable to fabricate a white LED, and its hydrophilic analogues can be a promising material for bioapplications.

Plastic antibodies tailored on quantum dots for an optical detection of myoglobin down to the femtomolar range

A highly sensitive fluorescence detection probe was developed by tailoring plastic antibodies on the external surface of aqueous soluble quantum dots (QDs). The target was Myoglobin (Myo), a cardiac biomarker that quenched the intrinsic fluorescent emission of cadmium telluride (CdTe) QDs capped with mercaptopropionic acid (CdTe-MPA-QDs). The QDs were incubated with the target protein and further modified with a molecularly-imprinted polymer (MIP) produced by radical polymerization of acrylamide and bisacrylamide. The main physical features of the materials were assessed by electron microscopy, dynamic light scattering (DLS), UV/Vis spectrophotometry and spectrofluorimetry. The plastic antibodies enabled Myo rebinding into the QDs with subsequent fluorescence quenching. This QD-probe could detect Myo concentrations from 0.304 to 571 pg/ml (50.6 fM to 95 pM), with a limit of detection of 0.045 pg/ml (7.6 fM). The proposed method was applied to the determination of Myo concentrations in synthetic human serum. The results obtained demonstrated the ability of the modified-QDs to determine Myo below the cut-off values of myocardial infarction. Overall, the nanostructured MIP-QDs reported herein displayed quick responses, good stability and sensitivity, and high selectivity for Myo, offering the potential to be explored as new emerging sensors for protein detection in human samples.

A novel label-free photoelectrochemical immunosensor based on NCQDs and Bi2S3 co-sensitized hierarchical mesoporous SnO2 microflowers for detection of NT-proBNP

A novel label-free PEC immunosensor based on NCQDs and Bi₂S₃ co-sensitized hierarchical mesoporous SnO₂ microflowers was developed for NT-proBNP detection.

An evaporation induced self-assembly approach to prepare polymorphic carbon dot fluorescent nanoprobes for protein labelling

Herein, we report a novel route to prepare polymorphic carbon dot fluorescent probes via the evaporation-induced self-assembly of glutaraldehyde and carbon dots, which first usually form carbon nanoclusters which then could self-assemble to form carbon nanocrystals, nanospheres or nanofibers in different ionic strength solutions at room temperature.

Metal Organic Frameworks Combining CoFe2O4 Magnetic Nanoparticles as Highly Efficient SERS Sensing Platform for Ultrasensitive Detection of N-Terminal Pro-Brain Natriuretic Peptide

N-terminal pro-brain natriuretic peptide (NT-proBNP) has been demonstrated to be a sensitive and specific biomarker for heart failure (HF). Surface-enhanced Raman spectroscopy (SERS) technology can be used to accurately detect NT-proBNP at an early stage for its advantages of high sensitivity, less wastage and time consumption. In this work, we have demonstrated a new SERS-based immunosensor for ultrasensitive analysis of NT-proBNP by using metal-organic frameworks (MOFs)@Au tetrapods (AuTPs) immobilized toluidine blue as SERS tag. Here, MOFs@AuTPs complexes were utilized to immobilize antibody and Raman probe for their excellent characteristics of high porosity, large surface area, and good biocompatibility which can obviously enhance the fixing amount of biomolecule. To simplify the experimental operation and improve the uniformity of the substrate, Au nanoparticles functionalized CoFe2O4 magnetic nanospheres (CoFe2O4@AuNPs) were further prepared to assemble primary antibody. Through sandwiched antibody-antigen interactions, the immunosensor can produce a strong SERS signal to detect NT-proBNP fast and effectively. With such design, the proposed immunosensor can achieve a large dynamic range of 6 orders of magnitude from 1 fg mL(-1) to 1 ng mL(-1) with a detection limit of 0.75 fg mL(-1). And this newly designed amplification strategy holds high probability for ultrasensitive immunoassay of NT-proBNP.

Quantum dot-layer-encapsulated and phenyl-functionalized silica spheres for highly luminous, colour rendering, and stable white light-emitting diodes

Although the quantum efficiencies of quantum dots (QDs) are approaching unity through advances in the synthesis of QD materials, their luminescence efficiencies after mixing with resin and thermal curing for white light-emitting diodes (LEDs) are seriously lowered because of aggregation and oxidation of QDs and poor adhesion of QDs to the resin. To overcome these problems, QD-layer-encapsulated and phenyl-functionalized silica (SQS(Ph)) spheres were synthesized and applied for white LEDs, whereby the QDs were homogeneously distributed at radial equidistance from the center and near the surface of approximately 100 nm-sized silica spheres and the surface was functionalized with phenylethyl groups. The inter-core distances of QDs were over ∼14 nm, which is over the limit (<10 nm) for Förster resonance energy transfer (FRET) that leads to photoluminescence (PL) reduction. This hierarchical nanostructure excludes a chance of FRET between QDs and provides the QDs a gradually refractive index matching environment, which yields ∼4-fold enhanced PL in SQS(Ph). More importantly, the SQS(Ph) acquired a highly adhesive property to silicone resin due to their phenyl functional group matching, which resulted in remarkably improved light extraction in white LEDs. When incorporated along with a yellow-emitting Y3Al5O12:Ce(3+) (YAG:Ce) phosphor and silicone resin on blue LED chips, the SQS(Ph) spheres presented significantly improved performance [luminous efficiency (LE) = 58.2 lm W(-1); colour rendering index Ra = 81.8; I/I0 = 0.98 after 60 h operation] than their original QDs (LE = 39.6 lm W(-1); Ra = 78.1; I/I0 = 0.91 after 60 h operation) under a forward bias current of 60 mA.