Lanthanide-based luminescent anti-counterfeiting materials are widely used in various kinds of products. However, the emission color of traditional lanthanide-based luminescent materials usually remains nearly unaltered upon different excitation lights, which may only work for single-level anti-counterfeiting. Herein, the NaYbF₄: 2%Er@NaYF₄ core/shell nanoplates (NPs) with "chameleon-like" optical behavior are developed. These NPs display single-band red or green downshifting (DS) emission upon excitation at 377 or 490 nm, respectively. Upon 980 nm excitation, the color of upconversion (UC) emission can be finely tuned from green to yellow, and to red with increasing the excitation power density from 0.1 to 4.0 W/cm². The proposed materials readily integrate the advantages of excitation wavelength-dependent DS single-band emissions and sensitive excitation power-dependent UC multicolor emissions in one and the same material, which has never been reported before. Particularly, the proposed NPs exhibit excellent performance as security labels on trademark tag and security ink on painting, thus revealing the great potential of these lanthanide-doped fluoride NPs in multilevel anti-counterfeiting applications.

CuInS₂ semiconductor nanocrystals (NCs) exhibit large absorption coefficient, size-dependent photoluminescence and low toxicity, making them excellent candidates in a variety of bioapplications. However, precise control of both their composition and morphology to improve the luminescent efficiency remains a great challenge via conventional direct synthesis. Herein, we present a novel low-temperature template synthesis of highly efficient luminescent CuInS₂ nanoprobes from In₂S₃ NCs via a facile cation exchange strategy. The proposed strategy enables synthesis of a series of CuInS₂ NCs with broad size tunability from 2.2 to 29.6 nm. Through rationally manipulating the stoichiometry of Cu/In, highly efficient luminescence of CuInS₂ with the maximum quantum yield of 28.6% has been achieved, which is about one order of magnitude improvement relative to that of directly synthesized NCs. By virtue of the intense emission of CuInS₂ nanoprobes, we exemplify their application in sensitive homogeneous biodetection for an important biomolecule of adenosine triphosphate (ATP) with the limit of detection down to 49.3 nM. Moreover, the CuInS₂ nanoprobes are explored for ATP-targeted cancer cell imaging, thus revealing their great potentials in the field of cancer diagnosis and prognosis.

Sensitive detection of cancer biomarker microRNAs (miRNAs) is of vital importance for cancer diagnosis and treatment. Nonetheless, the detection sensitivity in the existing miRNA bioassays is severely limited by the structural characteristics of miRNA (including small length and high sequence homology) because most of these methods are based on target amplification. Herein, we report a novel approach to sensitive and specific detection of low-abundance miRNA via a unique strategy of nanoprobe dissolution-enhanced fluorescence amplification, in which a capture probe featuring molecular beacon structure is designed. By means of this strategy, miRNA-21 was detected in a linear range from 10 fM to 100 pM with a detection limit as low as 1.38 fM. High selectivity of the newly developed biosensor was demonstrated by the good discrimination against a target with a single-base mismatch. Furthermore, this assay was used for the detection of miRNA-21 added into fetal bovine serum samples with the recovery in the range of 90.2%–108% and coefficients of variation below 10.1%, indicating its promising applications to RNA immunoassays and early cancer diagnosis.