Nanomaterials for ultrasensitive protein detection

Metal-organic framework-interfaced ELISA probe enables ultrasensitive detection of extracellular vesicle biomarkers

The enzyme-linked immunosorbent assay (ELISA) remains the prevailing method for quantifying protein biomarkers. Enzymatic signal generation and amplification are key mechanisms that govern its analytical performance. This study reports the synthesis and application of microscale metal-organic framework (MOF)/enzyme composite particles as a novel detection probe to substantially enhance the sensitivity of ELISA. An optimal one-pot approach was established to incorporate a substantial amount of streptavidin-horseradish peroxidase (SA-HRP) either within or on the surface of the metal-azolate framework (MAF-7) microparticles. This approach enables the labeling of a single sandwich antibody-antigen complex with numerous enzymes, which markedly amplifies the enzymatic colorimetric signal generation. Moreover, MAF-7 caging was found to enhance the reactivity of the caged HRP enzyme, further promoting the overall detection sensitivity of ELISA. Compared to other developments that are often associated with more complicated detection modalities, our method is compatible with standard immunoassays and commonly used photometrical signal detection. The implementation of this strategy in the detection of CD147 results in a remarkably low limit of detection of 2.8 fg mL-1, representing a 105-fold improvement compared to that obtained with the standard ELISA. Moreover, the heightened sensitivity of this technique renders it particularly suitable for diagnosing breast cancer, thus presenting a promising tool for the early detection of the disease in clinical settings.

Synthesis, Characterization, and Applications of Nanomaterials for Energy Conversion and Storage

Ever since the commencement of the Industrial Revolution in Great Britain in the mid-18th century, the annual global energy consumption from various fossil fuels, encompassing wood, coal, natural gas, and petroleum, has demonstrated an exponential surge over the past four centuries [...].

Tuning the plasmonic and catalytic signals of Au@Pt nanoparticles for dual-mode biosensing

Dual-mode biosensors have gained great attention due to their excellent detection accuracy provided by the mutual verification of output signals. However, current strategies for dual-mode sensing mainly rely on a signal probe exhibiting dual properties that may encounter unreliability. Herein, we report a dual-mode biosensing strategy by modulating the plasmonic and catalytic activities of nanoparticles through a surface growing approach. Ascorbic acid enables the growing of Au shell on Au@Pt NPs to tune both their peroxidase-like activity and plasmonic signal. Enzyme-catalyzed reactions can generate ascorbic acid to modulate the plasmonic and catalytic activities of nanoparticles. Combined with enzyme-linked immunosorbent assay, it enables dual-mode immunoassays of carbofuran with both a colorimetric readout by a spectrometer down to 0.1 ppb and a naked-eye readout of 5 ppb. This dual-mode biosensing technique advantages in tunable sensitivity and robustness, holding promise as an analytical platform for biomedical diagnosis and food safety.

Computer Vision-Based Artificial Intelligence-Mediated Encoding-Decoding for Multiplexed Microfluidic Digital Immunoassay

Digital immunoassays with multiplexed capacity, ultrahigh sensitivity, and broad affordability are urgently required in clinical diagnosis, food safety, and environmental monitoring. In this work, a multidimensional digital immunoassay has been developed through microparticle-based encoding and artificial intelligence-based decoding, enabling multiplexed detection with high sensitivity and convenient operation. The information encoded in the features of microspheres, including their size, number, and color, allows for the simultaneous identification and accurate quantification of multiple targets. Computer vision-based artificial intelligence can analyze the microscopy images for information decoding and output identification results visually. Moreover, the optical microscopy imaging can be well integrated with the microfluidic platform, allowing for encoding-decoding through the computer vision-based artificial intelligence. This microfluidic digital immunoassay can simultaneously analyze multiple inflammatory markers and antibiotics within 30 min with high sensitivity and a broad detection range from pg/mL to μg/mL, which holds great promise as an intelligent bioassay for next-generation multiplexed biosensing.

Plasmonic/magnetic nanoarchitectures: From controllable design to biosensing and bioelectronic interfaces

Controllable design of the nanocrystal-assembled plasmonic/magnetic nanoarchitectures (P/MNAs) inspires abundant methodologies to enhance light-matter interactions and control magnetic-induced effects by means of fine-tuning the morphology and ordered packing of noble metallic or magnetic building blocks. The burgeoning development of multifunctional nanoarchitectures has opened up broad range of interdisciplinary applications including biosensing, in vitro diagnostic devices, point-of-care (POC) platforms, and soft bioelectronics. By taking advantage of their customizability and efficient conjugation with capping biomolecules, various nanoarchitectures have been integrated into high-performance biosensors with remarkable sensitivity and versatility, enabling key features that combined multiplexed detection, ease-of-use and miniaturization. In this review, we provide an overview of the representative developments of nanoarchitectures that being built by plasmonic and magnetic nanoparticles over recent decades. The design principles and key mechanisms for signal amplification and quantitative sensitivity have been explored. We highlight the structure-function programmability and prospects of addressing the main limitations for conventional biosensing strategies in terms of accurate selectivity, sensitivity, throughput, and optoelectronic integration. State-of-the-art strategies to achieve affordable and field-deployable POC devices for early multiplexed detection of infectious diseases such as COVID-19 has been covered in this review. Finally, we discuss the urgent yet challenging issues in nanoarchitectures design and related biosensing application, such as large-scale fabrication and integration with portable devices, and provide perspectives and suggestions on developing smart biosensors that connecting the materials science and biomedical engineering for personal health monitoring.

Thickness-Sensing Sandwiched Plasmonic Biosensors Enable Label-Free Naked-Eye Antibody Quantification

Clinical serology assays for detecting the antibodies of the virus are time-consuming, are less sensitive/selective, or rely on sophisticated detection instruments. Here, we develop a sandwiched plasmonic biosensor (SPB) for supersensitive thickness-sensing via utilizing the distance-dependent electromagnetic coupling in sandwiched plasmonic nanostructures. SPBs quantitatively amplify the thickness changes on the nanoscale range (sensitivity: ∼2% nm^-1) into macroscopically visible signals, thereby enabling the rapid, label-free, and naked-eye detection of targeted biomolecular species (via the thickness change caused by immunobinding events). As a proof of concept, this assay affords a broad dynamic range (7 orders of magnitude) and a low LOD (∼0.3 pM), allowing for the extremely accurate SARS-CoV-2 antibody quantification (sensitivity/specificity: 100%/∼99%, with a portable optical fiber device). This strategy is suitable for high-throughput multiplexed detection and smartphone-based sensing at the point-of-care, which can be expanded for various sensing applications beyond the fields of viral infections and vaccination.

Nanomaterial-assisted microfluidics for multiplex assays

Simultaneous detection of different biomarkers from a single specimen in a single test, allowing more rapid, efficient, and low-cost analysis, is of great significance for accurate diagnosis of disease and efficient monitoring of therapy. Recently, developments in microfabrication and nanotechnology have advanced the integration of nanomaterials in microfluidic devices toward multiplex assays of biomarkers, combining both the advantages of microfluidics and the unique properties of nanomaterials. In this review, we focus on the state of the art in multiplexed detection of biomarkers based on nanomaterial-assisted microfluidics. Following an overview of the typical microfluidic analytical techniques and the most commonly used nanomaterials for biochemistry analysis, we highlight in detail the nanomaterial-assisted microfluidic strategies for different biomarkers. These highly integrated platforms with minimum sample consumption, high sensitivity and specificity, low detection limit, enhanced signals, and reduced detection time have been extensively applied in various domains and show great potential in future point-of-care testing and clinical diagnostics.

Microwave-Assisted Synthesis of Silver Nanoparticles for Multimode Colorimetric Sensing of Multiplex Metal Ions and Molecular Informatization Applications

Plasmonic materials have been widely used in chemo/biosensing and biomedicine. However, little attention has been paid to the application of plasmonic materials in terms of the transition from molecular sensing to molecular informatization. Herein, we demonstrated that silver nanoparticles (AgNPs) prepared through facile and rapid microwave heating have multimode colorimetric sensing capabilities to different metal ions (Cr³⁺, Hg²⁺, and Ni²⁺), which can be further transformed into interesting and powerful molecular information technology (massively parallel molecular logic computing and molecular information protection). The prepared AgNPs can quantitatively and sensitively detect Cr³⁺ and Hg²⁺ in actual water samples. The AgNPs' multimode-guided multianalyte sensing processing was further investigated to construct a series of basic logic gates and advanced cascaded logic circuits by considering the analytes as the inputs and the colorimetric signals (like color, absorbance, wavelength shift) as the outputs. Moreover, the selective responses and molecular logic computing ability of AgNPs were also utilized to develop molecular cryptosteganography for encrypting and hiding some specific information, which proves that the molecular world and the information world are interconnected and use each other. This research not only opens the door for the transition from molecular sensing to molecular informatization but also provides an excellent opportunity for the construction of the "metaverse" of the molecular world.

Engineered lanthanide-doped upconversion nanoparticles for biosensing and bioimaging application

Various fluctuations of intracellular ions, biomolecules, and other conditions in the physiological environment play crucial roles in fundamental biological processes. These factors are of great importance for analysis in biomedical detection. Nevertheless, developments of the simple, rapid, and accurate proof for specific detection still encounter major challenges. Upconversion nanoparticles (UCNPs), which could absorb multiple low-energy near-infrared light (NIR) photon excitation and emits high-energy photons caused by anti-Stokes shift, show unique upconversion luminescence (UCL) properties, for example, sharp emission band, high physicochemical stability like near-zero photobleaching, photo blinking in biological tissues, and long luminescence lifetime. Furthermore, the NIR used for the light source to excite UCNPs enable lower photo-damage effect and deeper penetration of tissue, and in the meantime, it can avoid the auto-fluorescence and light scattering from biological tissue interference. Thus, the lanthanide-doped UCNP-based functional platform with controlled structure, crystalline phase, size, and multicolor emission has become an appropriate nanomaterial for bioapplications such as biosensing, bioimaging, drug release, and therapies. In this review, the recent progress about synthesis and biomedical applications of UCNPs related to sensing and bioimaging is summarized. Firstly, the different luminescence mechanisms of the upconversion process are presented. Secondly, four of the most common methods for synthesizing UCNPs are compared as well as the advantages and disadvantages of these synthetic routes. Meanwhile, the surface modification of lanthanide-doped UCNPs was introduced to pave the way for their biochemistry applications. Next, this review detailed the biological applications of lanthanide-doped UCNPs, particularly in bioimaging, including UCL and multi-modal imaging and biosensing (monitoring intracellular ions and biomolecules). Finally, the challenges and future perspectives in materials science and biomedical fields of UCNPs are concluded: the low quantum yield of the upconversion process should be considered when they are executed as imaging contrast agents. And the biosafety of lanthanide-doped UCNPs needs to be evaluated.

Exploration of nanozymes in viral diagnosis and therapy

Nanozymes are nanomaterials with similar catalytic activities to natural enzymes. Compared with natural enzymes, they have numerous advantages, including higher physiochemical stability, versatility, and suitability for mass production. In the past decade, the synthesis of nanozymes and their catalytic mechanisms have advanced beyond the simple replacement of natural enzymes, allowing for fascinating applications in various fields such as biosensing and disease treatment. In particular, the exploration of nanozymes as powerful toolkits in diagnostic viral testing and antiviral therapy has attracted growing attention. It can address the great challenges faced by current natural enzyme-based viral testing technologies, such as high cost and storage difficulties. Therefore, nanozyme can provide a novel nanozyme-based antiviral therapeutic regime with broader availability and generalizability that are keys to fighting a pandemic such as COVID-19. Herein, we provide a timely review of the state-of-the-art nanozymes regarding their catalytic activities, as well as a focused discussion on recent research into the use of nanozymes in viral testing and therapy. The remaining challenges and future perspectives will also be outlined. Ultimately, this review will inform readers of the current knowledge of nanozymes and inspire more innovative studies to push forward the frontier of this field.

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.

Monolithic integration of nanorod arrays on microfluidic chips for fast and sensitive one-step immunoassays

Here, we present integrated nanorod arrays on microfluidic chips for fast and sensitive flow-through immunoassays of physiologically relevant macromolecules. Dense arrays of Au nanorods are easily fabricated through one-step oblique angle deposition, which eliminates the requirement of advanced lithography methods. We report the utility of this plasmonic structure to improve the detection limit of the cardiac troponin I (cTnI) assay by over 6 × 105-fold, reaching down to 33.9 fg mL-1 (~1.4 fM), compared with an identical assay on glass substrates. Through monolithic integration with microfluidic elements, the device enables a flow-through assay for quantitative detection of cTnI in the serum with a detection sensitivity of 6.9 pg mL-1 (~0.3 pM) in <6 min, which was 4000 times lower than conventional glass devices. This ultrasensitive detection arises from the large surface area for antibody conjugation and metal-enhanced fluorescent signals through plasmonic nanostructures. Moreover, due to the parallel arrangement of flow paths, simultaneous detection of multiple cancer biomarkers, including prostate-specific antigen and carcinoembryonic antigen, has been fulfilled with increased signal-to-background ratios. Given the high performance of this assay, together with its simple fabrication process that is compatible with standard mass manufacturing techniques, we expect that the prepared integrated nanorod device can bring on-site point-of-care diagnosis closer to reality.

In situ formation of Hg2+-coordinated fluorescent nanoparticles through a supramolecular polymer network used for efficient Hg2+ sensing and separation

There have been many new methods for synthesizing novel nanomaterials with unique functions. Herein, a novel strategy to form fluorescent nanoparticles in situ has been developed, and it can be applied to efficiently sense Hg2+ in living cells and also separate Hg2+ from water.

Advances in single-molecule fluorescent nanosensors

Single-molecule detection represents the ultimate sensitivity in measurement science with the characteristics of simplicity, rapidity, low sample consumption, and high signal-to-noise ratio and has attracted considerable attentions in biosensor development. In recent years, a variety of functional nanomaterials with unique chemical, optical, mechanical, and electronic features have been synthesized. The integration of single-molecule detection with functional nanomaterials enables the construction of novel single-molecule fluorescent nanosensors with excellent performance. Herein, we review the advance in single-molecule fluorescent nanosensors constructed by novel nanomaterials including quantum dots, gold nanoparticles, upconversion nanoparticles, fluorescent conjugated polymer nanoparticles, nanosheets, and magnetic nanoparticles in the past decade (2011-2020), and discuss the strategies, features, and applications of single-molecule fluorescent nanosensors in the detection of microRNAs, DNAs, enzymes, proteins, viruses, and live cells. Moreover, we highlight the future direction and challenges in this area. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > In Vitro Nanoparticle-Based Sensing Diagnostic Tools > Diagnostic Nanodevices.

Synthesis of Double-Layer Imprinted Polymers: BSA Depletion

A sensitive, rapid, and cost-effective method for quantitative analysis of proteins (e.g., detection, purification, depletion) for a wide variety of purposes is required in a number of areas, such as immunodiagnostics and biotechnology. Double-layer imprinting technique, which is carried out via polymerization of polymer solution with higher monomer concentration, covering and filling the supermacroporous structure of a pre-synthesized cryogel column with a lower monomer concentration, thus improving the surface area and adsorption capacity of final product, is a brand new approach for the application of cryogels in molecular imprinting technology. Within the scope of this chapter, BSA is selected as a model protein for the application of double-layer imprinting protocol. In this chapter, synthesis of double-layer BSA-imprinted and non-imprinted cryogel columns (BSA-DLIP and DLNIP, respectively) are described. In addition, characterization of synthesized columns and BSA depletion studies from aqueous solutions are described in detail, as well as selectivity of BSA-DLIPs for BSA, against competitors.

Cerium oxide nanofiber based electroanalytical sensor for TNF-α detection: Improved interfacial stability with Nafion

The present work is aimed at improving the adhesion of nanomaterials at the interface of solid state working electrodes. Towards this, herein, an efficient method has been proposed that requires the electrode interface to be decorated with an optimally thin layer of Nafion. This selectively permeable layer ensures the stability of the sensor interface, without hampering the transport of biomolecules and electrons. As a case study, here, electrospun Cerium oxide nanofiber (CeNF) modified Glassy carbon electrodes (GCE) have been used as the sensing interface, and stability and performance of the GCE/CeNF/Nafion interface is evaluated using analytical electrochemistry. The CeNF is synthesized via electrospinning and is characterized using X-ray diffraction spectroscopy, Thermal gravimetry, Fourier transform infrared spectroscopy, and Field emission scanning electron microscopy. Further, detection of sepsis specific biomarker TNF-α from spiked buffer samples is demonstrated, as a case study, towards evaluating the effect of Nafion on the interfacial sensitivity. The achieved LOD of GCE/CeNF and GCE/CeNF/Nafion for TNF-α detection were 2.8 fg/mL and 1.2 fg/mL, respectively. A comparative analysis between the Electrochemical impedance spectroscopic (EIS) results of the GCE/CeNF and the GCE/CeNF/Nafion interfaces confirms the improvement in stability, without affecting the sensitivity and the limiting detection.

Protein discrimination based on DNA induced perylene probe self-assembly

The development of a simple and effective method for the highly sensitive and selective discrimination of proteins is a subject of enormous interest. Herein, we report the construction of a novel fluorescence detection method based on a perylene probe for the highly efficient discrimination of multiple proteins. Single-stranded DNA (ssDNA) could induce aggregation of the perylene probe which caused quenching of probe fluorescence. After the addition of a protein, the protein could interact with the ssDNA-probe assembly complex with "turn-on" or further "turn-off" fluorescence response. A sensor array was designed based on the above phenomena which could realize the successful discrimination of proteins with 100% accuracy of cross validation. Nine representative proteins were successfully recognized. Moreover, it was observed that a protein could induce characteristic effect on the DNA-probe assembly with varying pH of assay buffer. Thus, different proteins showed unique fluorescence response towards assay buffers having different pH values. The assay buffer pH was then utilized as a sensing channel. Based on Linear Discriminant Analysis (LDA) nine proteins were successfully discriminated at the nanomolar concentration with 100% accuracy of cross validation. Furthermore, the sensor array also demonstrated differentiation of the nine proteins regardless of their concentration. The developed sensor array could also detect the proteins with great precision in human urine sample at a quite low concentration, which suggests its practical applicability for analysis of biological fluids.

Nanoporous aluminum oxide micropatterns prepared by hydrogel templating

Micropatterned nanoporous aluminum oxide arrays are prepared on silicon wafer substrates by using photopolymerized poly(dimethylacrylamide) hydrogels as porogenic matrices. Hydrogel micropatterns are fabricated by spreading the prepolymer mixture on the substrate, followed by UV photopolymerization through a micropatterned mask. The hydrogel is covalently bonded to the substrate surface. Al₂O₃ is produced by swelling the hydrogel in a saturated aluminum nitrate solution and subsequent thermal conversion/calcination. As a result, micropatterned porous Al₂O₃ microdots with heights in µm range and large specific surface areas up to 274 m² g^-1 are obtained. Hence, the hydrogel fulfills a dual templating function, namely micropatterning and nanoporosity generation. The impact of varying the photopolymerization time on the properties of the products is studied. Samples are characterized by light and confocal laser scanning microscopy, scanning electron microscopy, energy-dispersive x-ray spectrometry, and Kr physisorption analysis.

Four-in-One: Advanced Copper Nanocomposites for Multianalyte Assays and Multicoding Logic Gates

The usage of non-noble-metal nanomaterials for nanoprobes or functional modules is still a big challenge because of their poor stability, functionality, and surface plasmon resonance property. In this work, copper ion, mercaptosuccinic acid, and nanocrystalline cellulose are combined for facile one-step synthesis and self-assembly of ultrasmall copper nanoparticles to produce supercolloidal particles (NCC@MSA-Cu SPs). Cu SPs show advanced multifunctionality for fast point-of-care tests (POCTs) of four metal ions (Hg²⁺, Pb²⁺, Ag⁺, and Zr⁴⁺). These selective recognitions integrate four different chemical reaction mechanisms (ion etching, core-shell deposition, templated synthesis, and precipitation) to produce four distinct readout signals. The multisignal mode-guided multianalyte sensing strategy can effectively avoid interference that affects single signal mode-based sensing. Benefiting from the creative multi-input and multireadout abilities, the visual multicoding logic gates of OR, NOR, AND, and INHIBIT are built based on optical responses of Cu SPs.

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

Porphyrins as Colorimetric and Photometric Biosensors in Modern Bioanalytical Systems

Advances in porphyrin chemistry have provided novel materials and exciting technologies for bioanalysis such as colorimetric sensor array (CSA), photo-electrochemical (PEC) biosensing, and nanocomposites as peroxidase mimetics for glucose detection. This review highlights selected recent advances in the construction of supramolecular assemblies based on the porphyrin macrocycle that provide recognition of various biologically important entities through the unique porphyrin properties associated with colorimetry, spectrophotometry, and photo-electrochemistry.

On-Chip Detection of the Biomarkers for Neurodegenerative Diseases: Technologies and Prospects

Alzheimer's disease (AD), Parkinson's disease (PD) and glaucoma are all regarded as neurodegenerative diseases (neuro-DDs) because these diseases are highly related to the degeneration loss of functions and death of neurons with aging. The conventional diagnostic methods such as neuroimaging for these diseases are not only expensive but also time-consuming, resulting in significant financial burdens for patients and public health challenge for nations around the world. Hence early detection of neuro-DDs in a cost-effective and rapid manner is critically needed. For the past decades, some chip-based detection technologies have been developed to address this challenge, showing great potential in achieving point-of-care (POC) diagnostics of neuro-DDs. In this review, chip-based detection of neuro-DDs' biomarkers enabled by different transducing mechanisms is evaluated.

Sub-zeptomole Detection of Biomarker Proteins Using a Microfluidic Immunoarray with Nanostructured Sensors

We report here a low-cost electrochemical immunoarray with unprecedented sensitivity in the sub-zeptomole range with up to 5 log-decades dynamic range for accurate, multiplexed protein determinations. The microfluidic array features eight carbon sensors coated with a dense layer of 5 nm gold-nanoparticles derivatized with primary antibodies. Analyte proteins are captured by secondary antibody-poly-HPR (horseradish peroxidase) bioconjugates containing 400 HRP enzyme labels, with amplified amperometric peaks developed using H2O2 activator and hydroquinone mediator. Prostate cancer biomarkers prostate specific antigen (PSA), vascular endothelial growth factor-D (VEGF-D), ETS-related gene protein (ERG), and insulin-like growth factor-1 (IGF-1) were measured simultaneously with sub-fg/mL LODs (0.08-0.22 zmol). These proteins were determined in serum of postprostatectomy cancer patients which had much lower levels than prostate cancer patients without surgery. This immunoassay protocol makes thousands of low-abundance proteins accessible to quantitative measurements down to zeptomole levels.

Quantitative Detection and Imaging of Multiple Biological Molecules in Living Cells for Cell Screening

Because of insufficient information, a single biomarker is not sufficient for early diagnosis of cancer, whereas sensitive and selective detection of multiple biomolecules can significantly reduce analysis time, sample size, and accurately perform cell screening in early cancer. Therefore, the development of a noninvasive strategy that can simultaneously quantify multiple biomarkers (i.e., nucleic acids, proteins, and small molecules) in a single cell is particularly important. Herein, a universal sensing system (functional DNA@mesoporous silica nanoparticles (MSN)-Black Hole Quencher-rhodamine 6G (RhB), FDSBR), which is based on the combination of functionalized DNA and smart responsive nanomaterial, was successfully constructed. After incubation with the cells, different types of targets trigger the strand displacement reaction to release the fluorophore-labeled nucleic acids as the output signals to reflect the intracellular level of the telomerase and adenosine triphosphate (ATP), respectively. Simultaneously, intracellular miR-21 can be clearly indicated by the restored fluorescence of RhB when the caged double-stranded DNA was substituted into single-stranded DNA to open the pore. The concentrations of intracellular telomerase, miR-21, and ATP were identified successfully in three cell lines at the single-cell level. The results show that the contents of three biomolecules have significant differences in the three model cell lines and provide a promising route for developing innovative early disease diagnosis and cell screening assay.

Applying CRISPR-Cas12a as a Signal Amplifier to Construct Biosensors for Non-DNA Targets in Ultralow Concentrations

Efficient signal amplification is essential to construct ultrasensitive biosensors for biologically relevant species with abundant concomitant interferences. Here, we apply LbaCas12a as a signal amplifier to develop a versatile CRISPR-Cas12a platform to detect a wide range of analytes in ultralow concentrations. The platform relies on the indiscriminate single-stranded DNase activity of LbaCas12a, which recognizes single-stranded DNA intermediates generated by non-DNA targets down to femtomolar concentrations and subsequently enhances the fluorescence signal output. With the help of functional nucleotides (DNAzyme and aptamer), ultrasensitive bioassays for Pb²⁺ and Acinetobacter baumannii have been designed with a limit of detection down to ∼0.053 nM and ∼3 CFU/mL, respectively. It also allows simultaneous detection of four microRNAs (miRNAs) at a picomolar concentration without significant interferences by other counterparts, suggesting the potential of multiplexed miRNA expression profiles analysis in high throughput. Given the versatility and generality of the CRISPR-Cas12a platform, we expect the current work to advance the application of CRISPR-Cas-based platforms in bioanalysis and provide new insights into ultrasensitive biosensor design.

Luminescent Sm(III) complex bearing dynamic imine bonds as a multi-responsive fluorescent sensor for F- and PO43- anions together with Zn2+ cation in water samples

We have designed and synthesized a new luminescent mononuclear samarium (III) complex Sm-2_h based on the [1 + 1] Schiff-base macrocycle H₂L2_h, derived from the cyclocondensation reaction between dialdehyde and diamine precursors, and its exact architecture is determined to be [Sm(HL2_h) (NO₃)₂]. The sensing ability of complex Sm-2_h is carefully evaluated for various common inorganic ions in solution. It is shown that complex Sm-2_h is a multi-responsive fluorimetric sensor with high selectivity for F^- and PO₄^3- anions together with Zn²⁺ cation. The sensing process is rapid within 60 s for F^- and PO₄^3- ions and 300 s for Zn²⁺ ion. Further detailed responsive investigations suggest that its sensing behavior has excellent linear relationship between the fluorescence intensity (or absorption value) and ion concentration. The limit of detection (LOD) for sensing F^-, PO₄^3- and Zn²⁺ ions are as low as 2.61 μM (2.94 μM), 1.92 μM (1.64 μM) and 5.67 μM (3.53 μM), respectively, verified by fluorimetric (or colorimetric) titration experiments. ESI mass spectra prove that these efficient detections originate from the structure collapse of sensor Sm-2_h because of the ion-induced imine bond breakage. Moreover, sensor Sm-2_h shows excellent sensing performances for F^-, PO₄^3- and Zn²⁺ ions in real water samples, and we also have developed a convenient method to detect these three ions by use of the sensor impregnated test paper strips, providing rapid and distinguishable fluorimetric color changes. Therefore, the macrocyclic Sm(III) complex Sm-2_h could be regarded as a valuable candidate for monitoring F^-, PO₄^3- and Zn²⁺ ions in practical applications.

Dynamically Tunable Plasmonic Band for Reversible Colorimetric Sensors and Surface-Enhanced Raman Scattering Effect with Good Sensitivity and Stability

A colorimetric sensor based on plasmonic nanoparticles (NPs) is a promising and convenient detection tool, but its reproducibility and adjustability remain a challenge because the NPs are mainly random and uncontrollable. Herein, a colorimetric sensor with good reversibility and reproducibility was prepared by embedding the two-dimensional (2D) Au NP arrays on the surface of the polyacrylamide hydrogel film to form 2D Au NP arrays attached a hydrogel composite. For this composite, with the change of the interspacing distance of Au NPs driven by the swelling-shrinking behavior of the hydrogel carrier, the diffraction peaks faded away and plasmonic coupling peaks appeared, accompanied by a series of obvious color changes (iridescence ↔ violet ↔ golden yellow ↔ red), which can be correlated to the applied water content. Importantly, the composite had good reproducibility as a result of a highly ordered array structure. Additionally, this colorimetric sensor with a dynamically tunable plasmonic band can be used as a high-quality surface-enhanced Raman scattering (SERS) substrate because the gap distance of the Au NPs can be uniformly controlled. We demonstrated that, as the active gap distance decreased, the SERS signals can be significantly intensified. When the water content reached 40%, this SERS substrate exhibited high sensitivity (10^-10 M for 4-aminothiophenol and 10^-9 M for thiram) and good reproducibility (relative standard deviation of <20%) using the excitation laser of 785 nm because of the small gap between two adjacent Au NPs and the highly ordered periodic structure. Such 2D Au NP arrays attached to a hydrogel composite could be a new strategy to obtain a high-quality colorimetric sensor and dynamic SERS substrate.

Bioorthogonal Reactions Amplify Magnetic Nanoparticles Binding and Assembly for Ultrasensitive Magnetic Resonance Sensing

Conventional transverse relaxation time (T₂)-mediated magnetic resonance sensors (MRS) that utilizing the target-induces state change of magnetic nanoparticles (MNPs) mainly suffer from low sensitivity. Recent T₂-MRS that based on target-induced amount change of MNPs can achieve a higher sensitivity, but these sensors can hardly accommodate small molecules. We herein develop an ultrasensitive T₂-MRS that enable the detection of small molecules based on cascade bioorthogonal reactions (BRs)-realized MNPs binding and assembly. Benefiting from rapid and highly selective cascade BRs, a single small molecule target can not only increase MNPs binding but also assembly MNPs, which greatly amplifies T₂ signal for sensing based on both the state and amount change of MNPs for the first time. Our strategy is capable of sensing chlorpyrifos with a liner range of 0.1 ng/mL to 1000 ng/mL. We justify the practicability of our assay by detecting chlorpyrifos in apple and cabbage samples, whose accuracy is higher than that of enzyme linked immunosorbent assay. Our assay provides a cascade BRs-mediated MRS that can greatly broaden the use of T₂-based MRS for ultrasensitive sensing trace small molecules in complex samples.

Fluorous effect-induced emission of azido substituted poly(vinylidene fluoride) with high photostability and film formation

A family of unconventional fluorescent fluoropolymers have been synthesized, whose emission is attributed to the fluorous effects.

Recent advances in nanomaterial-enhanced enzyme-linked immunosorbent assays

This review highlights functional roles of nanomaterials for advancing conventional ELISA assays by serving as substrate-alternatives, enzyme-alternatives, or non-enzyme amplifiers.

Stomatocyte structural color-barcode micromotors for multiplex assays

Artificial micromotors have a demonstrated value in the biomedical area. Attempts to develop this technology tend to impart micromotors with novel functions to improve the values. Herein, we present novel structural color-barcode micromotors for the multiplex assays. We found that, by rapidly extracting solvent and assembling monodispersed nanoparticles in droplets, it could form stomatocyte colloidal crystal clusters, which not only showed striking structural colors and characteristic reflection peaks due to their ordered nanoparticles arrangement, but also provided effective cavities for the integration of functional elements. Thus, the micromotors with catalysts or magnetic elements in their cavities, as well as with the corresponding structural color coding, could be achieved by using the platinum and ferric oxide dispersed pre-gel to fill and duplicate the stomatocyte colloidal crystal clusters. We have demonstrated that the self-movement of these structural color-barcode micromotors could efficiently accelerate the mixing speed of the detection sample and greatly increase the probe–target interactions towards faster and more sensitive single or multiplex detection, and the magnetism of these barcode micromotors enables the flexible collection of the micromotors, which could facilitate the detection processes. These features make the stomatocyte structural color-barcode micromotors ideal for biomedical applications.

Sensitive and Multiplexed SERS Nanotags for the Detection of Cytokines Secreted by Lymphoma

The sensitive and simultaneous detection of cytokines will provide new insights into the physiological process and disease pathways due to the complex nature of cytokine networks. However, the key challenge is the lack of probes that can simultaneously detect multiple cytokines in a single sample. In this contribution, we proposed an alternative approach for sensitive cytokine detection in a multiplex manner by the use of a new set of surface-enhanced Raman spectroscopy (SERS) nanotags. Typically, the newly designed SERS nanotags are composed of gold nanoparticles as the core, tuneable Raman molecules as the reporters, and a thin silver layer as the shell. As demonstrated through rigorous numerical simulations, enhanced Raman signal is achieved due to a strong localization of light in the 0.2 nm thin, optically deep-subwavelength region between the Au core and the Ag shell. Sensitive detection of cytokines is realized by forming a sandwich immunoassay. The detection limit is down to 4.5 pg mL^-1 (S/N = 3). The specificity of the assay is proved as negligible signals were detected for the false targets. Furthermore, multiple cytokines are simultaneously detected in a single assay from the secretion of B-lymphocyte cell line (Raji) after concanavalin A (Con A) stimulation. The results indicate that our method holds a significant potential for sensitive and multiplexed detection of cytokines and offers the opportunity for future applications in clinical settings.

Low-fouling and highly sensitive fluorescence immunoassay of protein in serum based on the antifouling magnetic beads

Aim: A low-fouling and highly sensitive fluorescence immunoassay for protein detection in serum was proposed, and IgG was used as a model protein. Materials & methods: SH-PEG-NH2 serving as antifouling coating was conjugated with carboxyl Fe3O4 nanoparticles, and then, the thiol groups were conjugated with antibody via the covalent binding. IgG was captured through magnetic immunoreaction. Highly fluorescent quantum dots modified with streptavidin (SA-QDs) were united with biotin modified IgG antibody to form the sandwich structure. Results & conclusion: The fluorescence immunoassay was able to detect IgG with a detection limit of 3.89 ng/ml in buffer and 5.0 ng/ml in serum with satisfying selectivity and acceptable reproducibility, which demonstrated its potential application in quantitative analysis of real patient serum samples.

Two-step signal amplification for high-sensitivity detection of biomarkers using gold nanoparticle-based conjugates

The measurement of biomarkers in bodily fluids is extremely important for diagnosing disease, monitoring disease progression, and evaluating treatment efficacy. In this paper, we present a highly sensitive and compatible gold nanoparticle (AuNP)-based, two-step signal amplification system for biomarker detection. First, AuNPs were coated onto the surfaces of 96-well plates to generate rough surfaces, which enable immobilization of many more capture antibodies than a smooth substrate. As a result, detection sensitivity was enhanced significantly. Second, the horseradish peroxidase (HRP)-conjugated detection antibodies were labeled on large-size AuNPs, which increase the localized amounts of HRP and thus further lower the detection limit. Based on the consecutive signal amplification system, a high-sensitivity assay was achieved, with a LOD of 0.07 ng/mL for prostate-specific antigen (PSA). This assay was allowed to detect the PSA levels in clinical samples without changing the current standard immunoassay setups, showing great potential in many settings where immunoassays are needed.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Nanomaterials for luminescent detection of water and humidity

Significant advances of typical nanomaterials in the luminescent detection of water and humidity are presented.

Enzyme-Driven Switchable Fluorescence-SERS Diagnostic Nanococktail for the Multiplex Detection of Lung Cancer Biomarkers

Comprehensive profiling of multiple protein targets plays a critical role in deeper understanding of specific disease conditions associated with high heterogeneity and complexity. Herein, we present the design and fabrication of smart programmable nanoarchitectures, which could integrate clinically relevant diagnostic modalities for the multiplexed detection of most prevalent panel of disease biomarkers present in lung cancer. The multiplex nanoprobes were prepared by attaching dual-functional Raman-active fluorogens onto spherical gold nanoparticles through a peptide linker, Phe-Lys-Cys (FKC), which is engineered with a cathepsin B (cathB) enzyme cleavage site. The presence of cathB induces the scission of FKC upon homing into the cancer cells, resulting in the release of the initially latent fluorophores with a concomitant quenching of the surface-enhanced Raman signal intensity, thereby realizing an on-off switching between the fluorescence and Raman modalities. The enzyme-triggered switchable nanoprobes were utilized for the simultaneous detection of pathologically relevant lung cancer targets by tethering with specific antibody units. The multiplex-targeted multicolor coded detection capability of the antitags was successfully developed as a valid protein screening methodology, which can address the unmet challenges in the conventional clinical scenario for the precise and early diagnosis of lung cancer.

Hydrogels Incorporating Au@Polydopamine Nanoparticles: Robust Performance for Optical Sensing

Stimuli-responsive hydrogels (SRhG) that undergo response to physicochemical stimuli have been broadly applied in separation, biosensing, and drug delivery. Since, most of the SRhG are based on the structural behaviors (swelling or collapse). Herein, we describe a more simple and convenient colorimetric SRhG of polydopamine-coated gold nanoparticles (Au@PDA NPs) hydrogel. The newly developed SRhG is based on the in situ surface chemistry of Au@PDA NPs with core-shell structure embedding in agarose hydrogel. Silver ions can in situ form Ag NPs on surfaces of Au@PDA NPs (Ag_Au@PDA NPs with core-satellites like structure) at ambient conditions, which shift the localized surface plasmon resonance (LSPR) absorption peak and result in color change. The solid sensing phase of SRhG shows greatly improved stability and anti-interference ability comparing to that of solution phase sensing. With rational designs, Au@PDA NPs hydrogel shows great potential in optical sensing, for example, biothiol detection, and coupled with enzyme-cascade reaction for acetylcholinesterase activity detection and inhibitor assays with excellent sensitivity and selectivity.

Array-Based Protein Sensing Using an Aggregation-Induced Emission (AIE) Light-Up Probe

Protein detection and identification are important for the diagnosis of diseases; however, the development of facile sensing probes still remains challenging. Here, we present an array-based "turn on" protein-sensing platform capable of detecting and identifying proteins using aggregation-induced emission luminogens (AIEgens). The water-soluble AIEgens in which fluorescence was initially turned off showed strong fluorescence in the presence of nanomolar concentrations of proteins via restriction of the intramolecular rotation of the AIEgens. The binding affinities between the AIEgens and proteins were associated with various chemical functional groups on AIEgens, resulting in distinct fluorescent-signal outcomes for each protein. The combined fluorescence outputs provided sufficient information to detect and discriminate proteins of interest by linear discriminant analysis. Furthermore, the array-based sensor enabled classification of different concentrations of specific proteins. These results provide novel insight into the use of the AIEgens as a new type of sensing probe in array-based systems.

Fe-T1 Sensor Based on Coordination Chemistry for Sensitive and Versatile Bioanalysis

The main challenge of paramagnetic ions-mediated magnetic sensors is their relatively low sensitivity. In this study, we observe the amplification of longitudinal relaxation time (T₁) signal when Fe²⁺ transforms into Fe³⁺ followed by the coordination of potassium thiocyanate (KSCN) and develop a sensitive Fe-T₁ sensor based on the coordination chemistry between KSCN and Fe³⁺ to amplify the T₁ signal for detecting a series of targets, such as hydrogen peroxide, glucose, and antigen/antibody. We justify the practicability of our assay by successfully detecting tetracycline in milk samples and hepatitis C virus in clinical samples with satisfactory accuracy. This KSCN-mediated Fe-T₁ sensor not only realizes biochemical analysis and immunoassay with higher sensitivity but also retains many advantages of paramagnetic ions-mediated magnetic sensors (good stability and straightforward operation), which holds great promise for the detection of a range of targets of interest in complex samples.