By taking advantage of the optical properties of upconversion nanoparticles (UCNPs), we have designed a luminescence ratiometric nanosensor for measuring nitric oxide (NO) in biological fluids, live cells, and tissues. This nanoconjugate consists of a UCNP core with two strong fluorescence emission peaks at 540 and 656 nm as the upconversion fluorophore, NO-reactive rhodamine B-derived molecules (RdMs) encapsulated within the mesopores of the mSiO2 shell, and a β-cyclodextrin (βCD) layer on the exterior of the particle. Reaction of the analyte with the O-phenylenediamine of the RdM induces opening of the spiro-ring and is accompanied by an appearance of a strong rhodamine B (RdB) absorption band between 500 and 600 nm, which has spectral overlap with the green emission (540 nm) of the UCNPs. This results in an increase in the I656/I540 ratio and quantitatively correlates with [NO]. The assay is validated under clean buffer conditions as well as inserum and liver tissue slices obtained from mouse models.

In the present study, a novel fluorescence resonance energy transfer (FRET) strategy-based two-photon excited nanosensor via the assembly of two-photon dye-labeled peptides on the gold nanoparticle's surface has been developed and successfully applied in the caspase-3 imaging assay in living cells and ischemia–reperfusion surgery-treated rat liver tissue slices.

In the present study, a novel ratiometric SERS nanosensor via the assembly of 4-mercaptophenylboronic ester on the surface of gold nanorods has been developed and successfully applied in H2O2 imaging in living cells or cancer tissues.

In the present study, a novel two-photon nanoprobe has been developed and successfully applied in glutathione (GSH) imaging in cell apoptosis of cancer tissue.

A novel two-photon absorption (TPA) nanomicelle through the “host-guest” chemistry has been developed and successfully applied in tumor tissue imaging in this work.

Increasing the rate of target binding on the surface and enhancing the fluorescence signal restoration efficiency are critical to the desirable biomedical application of carbon nanomaterials, for example, single-walled carbon nanotubes (SWNTs). We describe here a strategy to increase the target binding rate and enhance the fluorescence signal restoration efficiency on the DNA-functionalized SWNT surface using a short complementary DNA (scDNA) strand. The scDNA causes up to a 2.5-fold increase in association rate and 4-fold increase in fluorescence signal restoration by its competitive assembly on the nanostructure’s surface and inducing a conformational change that extends the DNA away from the surface, making it more available to bind target nucleic acids. The scDNA-induced enhancement of binding kinetics and fluorescence signal restoration efficiency is a general phenomenon that occurred with all sequences and surfaces investigated. Through this competitive assembly strategy of scDNA, performance improvement of the carbon-nanomaterial-based biosensing platform for both in vitro detection and live cell imaging can be reached.Keywords: biosensors; carbon nanomaterials; competitive assembly; interface; short complementary DNA

Two-photon excitation (TPE) with near-infrared (NIR) photons as the excitation source has important advantages over conventional one-photon excitation (OPE) in the field of biomedical imaging. β-cyclodextrin polymer (βCDP)-based two-photon absorption (TPA) fluorescent nanomicelle exhibits desirable two-photon-sensitized fluorescence properties, high photostability, high cell-permeability and excellent biocompatibility. By combination of the nanostructured two-photon dye (TPdye)/βCDP nanomicelle with the TPE technique, herein we have designed a TPdye/βCDP nanomicelle-based TPA fluorescent nanoconjugate for enzymatic activity assay in biological fluids, live cells and tissues. This sensing system is composed of a trans-4-[p-(N,N-diethylamino)styryl]-N-methylpyridinium iodide (DEASPI)/βCDP nanomicelle as TPA fluorophore and carrier vehicle for delivery of a specific peptide sequence to live cell through fast endocytosis, and an adamantine (Ad)-GRRRDEVDK-BHQ2 (black hole quencher 2) peptide (denoted as Ad-DEVD-BHQ2) anchored on the DEASPI/βCDP nanomicelle’s surface to form TPA DEASPI/βCDP@Ad-DEVD-BHQ2 nanoconjugate by the βCD/Ad host–guest inclusion strategy. Successful in vitro and in vivo enzymatic activities assay of caspase-3 was demonstrated with this sensing strategy. Our results reveal that this DEASPI/βCDP@Ad-DEVD-BHQ2 nanoconjugate not only is a robust, sensitive and selective sensor for quantitative assay of caspase-3 in the complex biological environment but also can be efficiently delivered into live cells as well as tissues and act as a “signal-on” fluorescent biosensor for specific, high-contrast imaging of enzymatic activities. This DEASPI/βCDP@Ad-DEVD-BHQ2 nanoconjugate provides a new opportunity to screen enzyme inhibitors and evaluate the apoptosis-associated disease progression. Moreover, our design also provides a methodology model scheme for development of future TPdye/βCDP nanomicelle-based two-photon fluorescent probes for in vitro or in vivo determination of biological or biologically relevant species.

Lanthanide-based upconversion nanoparticles (UCNPs) are a new type of luminescent tags that show great application potential in biomedical fields. However, a major challenge when applying UCNPs in biomedical research is the lack of a versatile strategy to make water-dispersible and biocompatible UCNPs with high simplicity in functionalization. To address this problem, in the present work, we employed 6-phosphate-6-deoxy-β-cyclodextrin (βPCD) as the novel ligand to fabricate a versatile upconversion luminescent nanoplatform. Using βPCD as the surface ligand not only enhances the stability and biocompatibility of the UCNPs under physiological conditions but also enables simple conjugation with various functional molecules, such as organic dyes and biomolecules, via the host–guest interaction between those molecules and the cyclodextrin cavity. The conjugated upconversion nanoprobe then displays excellent capability in labeling the cancer cells and tumor tissue slices for luminescent imaging. These results demonstrate that the versatile cyclodextrin-functionalized upconversion nanoplatform appears particularly flexible for further modifications, indicating great potential for applications in biosensing and bioimaging.

Two-photon excitation (TPE) with near-infrared (NIR) photons as the excitation source have the unique properties of lower tissue autofluorescence and self-absorption, reduced photodamage and photobleaching, higher spatial resolution, and deeper penetration depth (>500 μm). Carbon nanomaterials, for example, graphene oxide (GO), have the advantages of good biocompatibility, efficient transporters into cells, protecting the carried DNA or peptides from enzymatic cleavage, and super fluorescence quenching efficiency. By combination of the nanostructured carbon materials with the TPE technique, herein we have designed an aptamer-two-photon dye (TPdye)/GO TPE fluorescent nanosensing conjugate for molecular probing in biological fluids, living cells, and zebrafish. This approach takes advantage of the exceptional quenching capability of GO for the proximate TP dyes and the higher affinity of single-stranded DNA on GO than the aptamer–target complex. Successful in vitro and in vivo detection of ATP was demonstrated with this sensing strategy. Our results reveal that the GO/Aptamer–TPdye system not only is a robust, sensitive, and selective sensor for quantitative detection of ATP in the complex biological environment but also can be efficiently delivered into live cells or tissues and act as a “signal-on” in vivo sensor for specific, high-contrast imaging of target biomolecules. Our design provides a methodology model scheme for development of future carbon nanomaterial-based two-photon fluorescent probes for in vitro or in vivo determination of biological or biologically relevant species.

A novel silver nanoparticle (AgNP)/DNA-two-photon dye (TP dye) conjugate was fabricated as a two-photon nanoprobe for biothiol imaging in live cells. DNA-templated silver nanoparticles are efficient quenchers and also provide a biocompatible nanoplatform for facile delivery of DNA into living cells. In the presence of biothiols (Cys, Hcy, or GSH), the strong interaction between the thiol group and silver results in the release of TP dye-labeled single-stranded DNA (ssDNA) from the AgNP surface and the subsequent fluorescence emission of the TP dye, thus enabling biothiols to be assayed. Our results reveal that the AgNP/DNA-TP dye nanosensing conjugate not only is a robust, sensitive, and selective sensor for quantitative detection of biothiols in the complex biological environment but also can be efficiently delivered into live cells and act as a “signal-on” sensor for specific, high-contrast imaging of target biomolecules. Our design provides a methodology for the development of future DNA-templated silver nanoparticle-based two-photon fluorescent probes for use in vitro or in vivo as biomolecular sensors for live-cell imaging.

A new approach for simple and rapid colorimetric detection of Hg2+ in aqueous solution is proposed based on Hg2+-induced aggregation of mononucleotides-stabilized gold nanoparticles.

In the present study, a novel two-photon nanoprobe has been developed and successfully applied in glutathione (GSH) imaging in cell apoptosis of cancer tissue.

In the present study, a novel ratiometric SERS nanosensor via the assembly of 4-mercaptophenylboronic ester on the surface of gold nanorods has been developed and successfully applied in H2O2 imaging in living cells or cancer tissues.

A novel two-photon absorption (TPA) nanomicelle through the “host-guest” chemistry has been developed and successfully applied in tumor tissue imaging in this work.

A new approach for simple and rapid colorimetric detection of Hg2+ in aqueous solution is proposed based on Hg2+-induced aggregation of mononucleotides-stabilized gold nanoparticles.