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 mSiO 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 I/I 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.

Herein, we describe a novel two-photon excitation/red emission-based ratiometric pH nanosensor consisting of a pH-sensitive two-photon dye and Tm3+-doped upconversion nanoparticles (UCNP). The fluorescence emission ratio between the dye (610 nm) and UCNPs (810 nm) (I610/I810) provides a linear indicator of pH values in the range from pH 4.0 to 6.5 with high sensitivity. These nanoprobes selectively accumulate in the lysosomes of cells, making them suitable for lysosomal pH tracking. This pH nanoprobe has been successfully applied in visualizing chemically stimulated changes of intracellular pH in living cells and tissues.

Photoelectrochemical (PEC) sensors are relatively new sensing platforms with high detection sensitivity and low cost. However, the current PEC biosensors dependent on ultraviolet or visible light as the exciting resource cause injuries to biological samples and systems, which restrains the applications in complicated matrixes. Herein, a near-infrared light (NIR)-initiated PEC biosensor based on NaYF 4 :Yb,Tm@NaYF 4 @ TiO 2 @CdS (csUCNRs@TiO 2 @CdS) was constructed for sensitive detection of acute myocardial infarction (AMI)-related miRNA-133a in an immobilization-free format coupled with a hybridization chain reaction and a redox circle signal amplification strategy. A low-energy 980 nm NIR incident laser was converted to 300−480 nm light to excite the adjacent TiO 2 @CdS photosensitive shell to generate photocurrent by NaYF 4 :Yb,Tm@NaYF 4 upconversion nanorods. Also, magnetic beads were employed for the homogeneous determination of target miRNA-133a to reduce the recognition steric hindrance and improve the detection sensitivity. The photocurrent response was positively correlated with the level of ascorbic acid as the energy donor to consume photoacoustic holes produced on the surface of csUCNRs@TiO 2 @CdS, which was generated by alkaline phosphatase catalyzation and regenerated by tris(2-carboxyethyl) phosphine reduction upon the appearance of miRNA-133a. Exerting a NIR-light-driven and immobilization-free strategy, the asconstructed biosensor displayed linearly sensitive and selective determination of miRNA-133a with a detection limit of 36.12 aM. More significantly, the assay method provided a new concept of the PEC sensing strategy driven by NIR light to detect diverse biomarkers with pronounced sensitivity, light stability, and low photodamage.

The three-layer structure model of the fiber Bragg grating is proposed in this paper. And through experimental study and reasoning calculation to verify the three layer structure of the optical waveguide model, so the sensitivity characteristic of the Bragg wavelength to the refractive index of chemical solution is obtained. And the relationships between the concentration and the shift of Bragg wavelength of sucrose, ethanol, and Nacl solution are achieved. Finally the shifts of the Bragg wavelength with the external concentration are obtained by experiments. A kind of simple structure, small size, good stability, high sensitivity chemical concentration sensor is obtained.