A double responsive smart upconversion fluorescence sensing material for glycoprotein

Molecularly imprinted thermosensitive probe based on fluorescent advanced glycation end products to detect α-dicarbonyl compounds and inhibit pyrraline formation

A thermal-sensitive molecularly imprinted optosensing probe based on fluorescent advanced glycation end products (AGEs) was prepared by one-pot hydrothermal synthesis. Carbon dots (CDs) derived from fluorescent AGEs were used as the luminous centers, while molecularly imprinted polymers (MIPs) were wrapped outside of the CDs to form specific target recognition sites to highly selectively adsorb the intermediate product of AGEs of 3-deoxyglucosone (3-DG). Thermosensitive N-isopropylacrylamide (NIPAM) was combined with acrylamide (AM) as co-functional monomers, and ethylene glycol dimethacrylate (EGDMA) was chosen as a cross-linker for targeting identification and detection of 3-DG. Under optimal conditions, the fluorescence of MIPs could be gradually quenched with the adsorption of 3-DG on the surface of MIPs in the linear range of 1-160 μg/L, and the detection limit was 0.31 μg/L. The spiked recoveries of MIPs ranged from 82.97 to 109.94% in two milk samples, and the relative standard deviations were all less than 1.8%. In addition, the inhibition rate for non-fluorescent AGEs of pyrraline (PRL) was 23% by adsorbing 3-DG in the simulated milk system of casein and D-glucose, indicating that temperature-responsive MIPs not only could detect the dicarbonyl compound 3-DG quickly and sensitively, but also had an excellent inhibitory effect on AGEs.

Advances in fluorescence sensing enabled by lanthanide-doped upconversion nanophosphors

Lanthanide-doped upconversion nanoparticles (UCNPs), characterized by converting low-energy excitation to high-energy emission, have attracted considerable interest due to their inherent advantages of large anti-Stokes shifts, sharp and narrow multicolor emissions, negligible autofluorescence background interference, and excellent chemical- and photo-stability. These features make them promising luminophores for sensing applications. In this review, we give a comprehensive overview of lanthanide-doped upconversion nanophosphors including the fundamental principle for the construction of UCNPs with efficient upconversion luminescence (UCL), followed by state-of-the-art strategies for the synthesis and surface modification of UCNPs, and finally describing current advances in the sensing application of upconversion-based probes for the quantitative analysis of various analytes including pH, ions, molecules, bacteria, reactive species, temperature, and pressure. In addition, emerging sensing applications like photodetection, velocimetry, electromagnetic field, and voltage sensing are highlighted.

Lanthanide upconversion and downshifting luminescence for biomolecules detection

Biomolecules play critical roles in biological activities and are closely related to various disease conditions. The reliable, selective and sensitive detection of biomolecules holds much promise for specific and rapid biosensing. In recent years, luminescent lanthanide probes have been widely used for monitoring the activity of biomolecules owing to their long luminescence lifetimes and line-like emission which allow time-resolved and ratiometric analyses. In this review article, we concentrate on recent advances in the detection of biomolecule activities based on lanthanide luminescent systems, including upconversion luminescent nanoparticles, lanthanide-metal organic frameworks, and lanthanide organic complexes. We also introduce the latest remarkable accomplishments of lanthanide probes in the design principles and sensing mechanisms, as well as the forthcoming challenges and perspectives for practical achievements.

Exploring the use of upconversion nanoparticles in chemical and biological sensors: from surface modifications to point-of-care devices

Upconversion nanoparticles (UCNPs) have emerged as promising luminescent nanomaterials due to their unique features that allow the overcoming of several problems associated with conventional fluorescent probes. Although UCNPs have been used in a broad range of applications, it is probably in the field of sensing where they best evidence their potential. UCNP-based sensors have been designed with high sensitivity and selectivity, for detection and quantification of multiple analytes ranging from metal ions to biomolecules. In this review, we deeply explore the use of UCNPs in sensing systems emphasizing the most relevant and recent studies on the topic and explaining how these platforms are constructed. Before diving into UCNP-based sensing platforms it is important to understand the unique characteristics of these nanoparticles, why they are attracting so much attention, and the most significant interactions occurring between UCNPs and additional probes. These points are covered over the first two sections of the article and then we explore the types of fluorescent responses, the possible analytes, and the UCNPs' integration with various material types such as gold nanostructures, quantum dots and dyes. All the topics are supported by analysis of recently reported sensors, focusing on how they are built, the materials' interactions, the involved synthesis and functionalization mechanisms, and the conjugation strategies. Finally, we explore the use of UCNPs in paper-based sensors and how these platforms are paving the way for the development of new point-of-care devices.

Near-Infrared-Triggered Upconverting Nanoparticles for Biomedicine Applications

Due to the unique properties of lanthanide-doped upconverting nanoparticles (UCNP) under near-infrared (NIR) light, the last decade has shown a sharp progress in their biomedicine applications. Advances in the techniques for polymer, dye, and bio-molecule conjugation on the surface of the nanoparticles has further expanded their dynamic opportunities for optogenetics, oncotherapy and bioimaging. In this account, considering the primary benefits such as the absence of photobleaching, photoblinking, and autofluorescence of UCNPs not only facilitate the construction of accurate, sensitive and multifunctional nanoprobes, but also improve therapeutic and diagnostic results. We introduce, with the basic knowledge of upconversion, unique properties of UCNPs and the mechanisms involved in photon upconversion and discuss how UCNPs can be implemented in biological practices. In this focused review, we categorize the applications of UCNP-based various strategies into the following domains: neuromodulation, immunotherapy, drug delivery, photodynamic and photothermal therapy, bioimaging and biosensing. Herein, we also discuss the current emerging bioapplications with cutting edge nano-/biointerfacing of UCNPs. Finally, this review provides concluding remarks on future opportunities and challenges on clinical translation of UCNPs-based nanotechnology research.

A multifunctional near-infrared fluorescent sensing material based on core-shell upconversion nanoparticles@magnetic nanoparticles and molecularly imprinted polymers for detection of deltamethrin

The construction of multifunctional sensors has attracted considerable attention due to their multifunctional properties, such as high sensitivity and rapid detection. Herein, near-infrared multifunctional fluorescent sensing materials based on core-shell upconversion nanoparticle@magnetic nanoparticle and molecularly imprinted polymers were synthesized for rapid detection of deltamethrin. The difunctional core-shell upconversion nanoparticle@magnetic nanoparticle was introduced as the optical signal and rapid separator. Firstly, the difunctional core-shell materials were prepared through solvothermal method. Then, molecularly imprinted polymers (MIPs) as recognition elements for deltamethrin were coated on the surface of upconversion nanoparticle@magnetic nanoparticle through polymerization. The structure and recognition characterizations of multifunctional fluorescent sensing materials were evaluated. Under optimal condition, the imprinting factor of sensing materials was 3.63, and the fluorescence intensity of sensing materials decreased linearly with increasing concentration of deltamethrin from 0.001 to 1 mg L^-1 with a detection limit of 0.749 μg L^-1, and a relative standard deviation of 3.10% was obtained with 5 mg L^-1 deltamethrin. The sensing materials showed a high selectivity and were successfully utilized for the detection of deltamethrin in grapes and cabbages; the results showed that the recoveries for two samples obtained were 95.6-102% and 91.8-105%.

Fluorescent nanosensor designing via hybrid of carbon dots and post-imprinted polymers for the detection of ovalbumin

We reported a facile strategy to assemble a ratiometric nanosensor for the ovalbumin (OVA) fluorescence determination and meanwhile it can be utilized for selective visual identification by naked eyes with fluorescent test papers under 365 nm UV lamp. The nanosensor was prepared through simply mixing blue color carbon dots (CDs) and green color core-shell imprinted polymers. Blue CDs were used directly as the internal reference without participating in the imprinting process and modified molecularly imprinted polymers (MIPs) were synthesized by post-imprinting, using fluorescein isothiocyanate (FITC) as fluorescence enhanced signal. Upon the addition of different concentrations of OVA, the fluorescence intensity of FITC was enhanced, while the fluorescence intensity of CDs was almost unchanged, leading to a detection limit as low as 15.4 nM. Accordingly, the fluorescence color was gradually changed from blue to dark olive green to green with naked eyes observation. Moreover, the ratiometric nanosensor was successfully applied to detect OVA in the human urine samples with satisfactory recoveries attaining of 92.0-104.0% with relative standard deviation (RSD) of 3.3-3.9% and 93.3-101.0% with RSDs of 2.7-3.8% for the spiked chicken egg white samples. This strategy reported here opens a novel pathway for biomacromolecule detection in real applications and can realize the visual observation on fluorescent test papers.

Boronate affinity material-based sensors for recognition and detection of glycoproteins

This review comprehensively presents the current overview and development potential of BAMs-based sensors for glycoprotein recognition and detection.

Surfactant-Sensitized Covalent Organic Frameworks-Functionalized Lanthanide-Doped Nanocrystals: An Ultrasensitive Sensing Platform for Perfluorooctane Sulfonate

Perfluorooctane sulfonate (PFOS) known as a persistent organic pollutant has been attracting great interests due to its potential ecotoxicity. An approach capable of sensing ultra-trace PFOS is in urgent demand. Here, we developed an approach for highly sensitive sensing PFOS using surfactant-sensitized covalent organic frameworks (COFs)-functionalized upconversion nanoparticles (UCNPs) as a fluorescent probe. COFs-functionalized UCNPs (UCNPs@COFs) were obtained by solvothermal growth of 1,3,5-triformylbenzene and 1,4-phenylenediamine on the surface of UCNPs. COF's layer on the surface of UCNPs not only provides recognition sites for PFOS but also improves the fluorescence quantum yields from 2.15 to 5.12%. Trace PFOS can quench the fluorescence emission of UCNPs@COFs at 550 nm due to the high electronegativity of PFOS. Moreover, the fluorescence quenching response can be significantly strengthened in the presence of a surfactant, which causes more sensitivity. The fluorescence quenching degrees (F 0 - F) of the system are linear with the concentration of PFOS in the range of 1.8 × 10-13 to 1.8 × 10-8 M. The present sensor can sensitively and selectively detect PFOS in tap water and food packing with the limit of detection down to 0.15 pM (signal-to-noise ratio = 3), which is comparable to that of the liquid chromatography-mass spectrometry technique. The proposed approach realized a simple, fast, sensitive, and selective sensing PFOS, showing potential applications in various fields.

Ultrasensitive Microfluidic Paper-Based Electrochemical Biosensor Based on Molecularly Imprinted Film and Boronate Affinity Sandwich Assay for Glycoprotein Detection

In this work, we proposed a strategy that combined molecularly imprinted polymers (MIPs) and hybridization chain reaction into microfluidic paper-based analytical devices for ultrasensitive detection of target glycoprotein ovalbumin (OVA). During the fabrication, Au nanorods with a large surface area and superior conductibility were grown on paper cellulosic fiber as a matrix to introduce a boronate affinity sandwich assay. The composite of MIPs including 4-mercaptophenylboronic acid (MPBA) was able to capture target glycoprotein OVA. SiO₂@Au nanocomposites labeled MPBA and cerium dioxide (CeO₂)-modified nicked DNA double-strand polymers (SiO₂@Au/dsDNA/CeO₂) as a signal tag were captured into the surface of the electrode in the presence of OVA. An electrochemical signal was generated by using nanoceria as redox-active catalytic amplifiers in the presence of 1-naphthol in electrochemical assays. As a result, the electrochemical assay was fabricated and could be applied in the detection of OVA in the wide linear range of 1 pg/mL to 1000 ng/mL with a relatively low detection limit of 0.87 pg/mL (S/N = 3). The results indicated that the proposed platform possessed potential applications in clinical diagnosis and other related fields.

A biomimetic fluorescent nanosensor based on imprinted polymers modified with carbon dots for sensitive detection of alpha-fetoprotein in clinical samples

A biomimetic fluorescent nanosensor based on molecularly imprinted polymers modified with carbon dots (CDs@MIPs) has been prepared for rapid, selective and sensitive detection of alpha-fetoprotein (AFP) in clinical samples.

Upconversion fluorescent nanoparticles based-sensor array for discrimination of the same variety red grape wines

A fluorescent sensor array composed of upconversion nanomaterials to distinguish the same variety of red grape wines was constructed.

Boronic acid functionalized g-C3N4 nanosheets for ultrasensitive and selective sensing of glycoprotein in the physiological environment

As important biomarkers, glycoprotein sensing is frequently facilitated by boronic acid binding with its cis-diols. However, boronic acid based sensors suffer from drawbacks of alkali restriction and/or sensitivity limitation. Herein, we report boronic acid decorated g-C₃N₄ nanosheets (B-g-CN) with a Wulff-type boronic acid feature, which selectively bind glycoprotein under physiological conditions. Meanwhile, the binding causes significant enhancement of the B-g-CN nanosheet fluorescence, providing the basis for glycoprotein sensing. With IgG as a model, a detection limit (LOD) of 2.2 nM (3σ/s, n = 11) was obtained within a linear range of 6.7-67 nM. The LOD was further improved to 52 pM subject to enrichment of the nanosheets, which well enables IgG assay in human urine samples. Moreover, it was successful in imaging endogenous and exogenous glycoproteins in living cells.

Bistable [2]rotaxane encoding an orthogonally tunable fluorescent molecular system including white-light emission

By combining a rotaxane-type molecular switch and traditional fluorescent switch, an orthogonally tunable fluorescent molecular system was constructed, which can generate multicolor fluorescence including white light.

Stimuli-responsive fluorescence switching of cyanostilbene derivatives: ultrasensitive water, acidochromism and mechanochromism

A novel donor–π–acceptor structure stimuli-responsive fluorescent material of (Z)-2-(4′-(diphenylamino)-[1,1′-biphenyl]-4-yl)-3-(pyridin-2-yl)acrylonitrile (oN-TPA) was designed and synthesized, with the cyano-group and pyridine as the acceptors (A) and triphenylamine as the donor (D). oN-TPA exhibits an obvious solvatochromic effect and the excited state is confirmed to be a hybridized local and charge-transfer (HLCT) state that simultaneously possesses the locally-excited (LE) state and charge transfer (CT) state characters. The LE state ensures relatively high fluorescence efficiency while the CT state provides multi-stimuli responsive fluorescence behaviors because it is easily tuned by the surrounding environment. Firstly, oN-TPA exhibits “on–off–on” fluorescence properties in the mixture of water/tetrahydrofuran (THF) with the increasing water content. For the “on–off” part, a good linear relationship between fluorescence intensity and water fraction is achieved, which is ascribed to the synergistic effect of protons in water and intramolecular charge-transfer (ICT) effect depending on solvent polarity. The “off–on” part demonstrates the aggregation-induced enhanced emission (AIEE) character of oN-TPA. Secondly, oN-TPA can be used as a protonic acid sensor to detect trifluoroacetic acid (TFA) in solvent and HCl vapour in the solid state due to the binding of the proton to the pyridine group. Finally, oN-TPA presents remarkable and reversible mechanochromic fluorescence switching between 552 nm and 642 nm (90 nm red-shift) during the pressurizing–depressurizing process. This work not only comprehensively demonstrates the stimuli-responsive fluorescence behaviors of oN-TPA, but also provides a D–π–A structure fluorescent material possessing potential applications in detection and sensing with remarkable fluorescence changes.

A donor–acceptor dye exhibits high luminescence efficiency and high-contrast piezochromism with HLCT properties. The doped films show the ratiometric photo-luminescence peak shift under high pressure, interestingly, making them piezo-sensors.

Quantification of antigen by digital domain analysis of integrated nanogap biosensors

Nanogap biosensor shows a distinct conduction change upon sandwich-type immobilization of gold nanoparticle probes onto the gap region in the presence of target biomolecules. Although this large conductance change could be advantageous in distinguishing signal on or off devices, since the extent of conductance change is quite irregular even at the same analyte concentrations, it fails to extract quantitative information from its level of conductance change. In other words, the conductance change of a single device does not reflect the concentration of the target molecule. In this study, we introduce an alternative approach of interpreting the concentration of target molecules using digital domain analysis of integrated nanogap devices, where the fraction of signal-on-devices, or on-device-percentage (ODP), was translated into the concentration of the target molecule. The ODP was found to be closely related to the number density of the immobilized probes and, therefore, to be an excellent measure of the analyte concentration, which was demonstrated in the immuno-selective detection and quantification of influenza A hemagglutinin and prostate specific antigen.

Ultrasensitive Electrochemical Detection of Glycoprotein Based on Boronate Affinity Sandwich Assay and Signal Amplification with Functionalized SiO2@Au Nanocomposites

Herein we propose a multiple signal amplification strategy designed for ultrasensitive electrochemical detection of glycoproteins. This approach introduces a new type of boronate-affinity sandwich assay (BASA), which was fabricated by using gold nanoparticles combined with reduced graphene oxide (AuNPs-GO) to modify sensing surface for accelerating electron transfer, the composite of molecularly imprinted polymer (MIP) including 4-vinylphenylboronic acid (VPBA) for specific capturing glycoproteins, and SiO₂ nanoparticles carried gold nanoparticles (SiO₂@Au) labeled with 6-ferrocenylhexanethiol (FcHT) and 4-mercaptophenylboronic acid (MPBA) (SiO₂@Au/FcHT/MPBA) as tracing tag for binding glycoprotein and generating electrochemical signal. As a sandwich-type sensing, the SiO₂@Au/FcHT/MPBA was captured by glycoprotein on the surface of imprinting film for further electrochemical detection in 0.1 M PBS (pH 7.4). Using horseradish peroxidase (HRP) as a model glycoprotein, the proposed approach exhibited a wide linear range from 1 pg/mL to 100 ng/mL, with a low detection limit of 0.57 pg/mL. To the best of our knowledge, this is first report of a multiple signal amplification approach based on boronate-affinity molecularly imprinted polymer and SiO₂@Au/FcHT/MPBA, exhibiting greatly enhanced sensitivity for glycoprotein detection. Furthermore, the newly constructed BASA based glycoprotein sensor demonstrated HRP detection in real sample, such as human serum, suggesting its promising prospects in clinical diagnostics.

Multiple Stimuli-Responsive Fluorescence Behavior of Novel Polyamic Acid Bearing Oligoaniline, Triphenylamine, and Fluorene Groups

Multiple stimuli-responsive fluorescent materials have gained increasing attention for their fundamental investigation and intelligent applications. In this work, we report design and synthesis of a novel polyamic acid bearing oligoaniline, triphenylamine, and fluorene groups, which served as sensitive units and fluorescence emission unit, respectively. The resulting polymer exhibits multiple stimuli-responsive fluorescence switching behavior triggered by redox species, pH, electrochemical, and pressure stimuli. Every fluorescence switching mechanism upon each stimulus was studied in detail. The interactions and energy transfer between sensitive units and emission unit are largely responsible for this fascinating fluorescent switching behavior. This work provides a deep understanding of the optical switching essence upon these stimuli, opening the way for the development of new fluorescent sensing applications.