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There is a close correlation between body health and the level of biofluid-derived metal ions, which makes it an attractive model analyte for noninvasive health monitoring. The present work has developed a novel nose/tongue-mimic chemosensor array based on bioinspired polydopamine/polyethylenimine copolymers (PDA/PEI ) for label-free fluorescent determination of metal ions in biofluids. Three types of PDA/PEI (PDA/PEI, PDA/PEI, and PDA/PEI) were prepared by using different concentrations of PEI to construct the proposed sensor array, which would lead to unique fluorescence response patterns upon challenged with metal ions for their pattern discrimination. The results show that as few as 3 PDA/PEI sensors can successfully realize the largescale sensitive detection of metal ions in biofluids. Moreover, we have demonstrated that PDA/PEI sensors are qualified for lifetime-based pattern discrimination application. Furthermore, the sensors can distinguish between different concentrations of metal ions, as well as a mixture of different metal ions in biofluids, even the mixtures with different valence states. The method promises the simple, rapid, sensitive, and powerful discrimination of metal ions in accessible biofluids, showing the potential applications in the diagnosis of metal ion-involved diseases.

Recent years have witnessed the rapid development of pattern-based sensors due to their potential to detect and differentiate a wealth of analytes with only few probes. However, no one has found or used the combination of DNA and terbium(III) (Tb) as a pattern recognition system for large-scale mix-and-measure assays. Here we report for the first time that DNA-sensitized Tb (DNA/Tb), as a label-free and versatile "chemical nose/tongue", can be employed for wide-scale time-gated luminescent (TGL) monitoring of metal ions covering nearly the entire periodic table in a cost-effective fashion. A series of guanine/thymine (G/T)-rich DNA ligands was screened to sensitize the luminescence of Tb (referring to the antenna effect) as smart pattern responders to metal ions in solution, and metal ion-DNA interactions can differentially alter the antenna effect of DNA toward Tb as pattern signals. Our results show that as few as 3 DNA/Tb label-free sensors could successfully discriminate 49 analytes, including alkali-metal ions, alkaline-earth-metal ions, transition/post-transition metal ions, and lanthanide ions. A blind test with 49 metals further confirmed the discriminating power of DNA/Tb sensors. Moreover, the lifetime-based pattern recognition application using DNA/Tb sensors was also demonstrated. This DNA/Tb pattern recognition strategy could be extended to construct a series of "chemical noses/tongues" for monitoring various biochemical species by using different responsive DNA ligands, thus promising a versatile and powerful tool for a sensing application and investigation of DNA-involving molecular interactions.

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Dual-mode optical assays are becoming more popular and attractive because they would provide robust detailed information in biochemical analysis. We herein unveil a novel dual-mode optical (i.e., UV-vis absorption and fluorescence) method for multifunctional sensing of phosphate compounds (PCs) (e.g., nucleotides and pyrophosphate) based on pattern recognition, which innovatively employs only one kind of porphyrin/lanthanide-doped upconversion nanoparticles (Ln-UCNPs) hybrid integrated with a facile pH-regulated strategy as the sensor array. An easy-to-obtain porphyrin hydrate (tetraphenylporphyrin tetrasulfonic acid hydrate, TPPS) can assemble onto the ligand-free Ln-UCNPs to construct the organic/inorganic hybrid (TPPS/Ln-UCNPs), leading to a new absorption band to quench the upconversion fluorescence of Ln-UCNPs due to fluorescence resonance energy transfer (FRET). The dual-mode optical performances of TPPS/Ln-UCNPs are characteristically correlated with the pH in aqueous solution. Thus, as a proof-of-concept design, three types of TPPS/Ln-UCNPs (TPPS/Ln-UCNPs, TPPS/Ln-UCNPs, and TPPS/Ln-UCNPs) were prepared by using buffers with different pH (at 4, 4.5, and 5) to form our proposed sensor array, which would result in individual dual-mode optical response patterns upon being challenged with PCs for their pattern recognition through a competitive mechanism between TPPS and PCs. The results show that three TPPS/Ln-UCNPs sensors can successfully permit the sensitive detection of 14 PCs and differentiate them between different concentrations, as well as a mixture of them. The pH-dependent TPPS/Ln-UCNPs promises the simple, yet powerful discrimination of PCs via pattern recognition, would prospectively stimulate and expand the use of organic/inorganic hybrid toward more biosensing applications.

Screening functional DNA that can fruitfully interact with metal ions is a long-standing hot topic in the fields of biotechnology, medicine, and DNA-based sensors. In this paper, we focus on the chemistry of europium(III) (Eu) coupled with single-stranded DNA (ssDNA), and we innovatively unveil that cytosine- and thymine-rich ssDNA oligomers (e.g., C and T) can be effective antenna ligands to sensitize the luminescence of Eu. Luminescence lifetime spectroscopy, circular dichroic (CD) spectroscopy, and isothermal titration calorimetry (ITC) have been used to systematically characterize the interaction involved between Eu and ssDNA. In light of the resultant sequence-dependent performances, the long luminescence lifetime Eu/ssDNA-based label-free and versatile probes are further devised as a pattern distinction system for time-resolved luminescent (TRL) sensing applications. The interactions of metal ions and ssDNA can distinctively shift the antenna effect of ssDNA toward Eu as accessible pattern signals. As a result, as few as two Eu/ssDNA label-free TRL probes can discriminate 17 metal ions via principal component analysis (PCA). In addition, thiols can readily capture metal ions to switch the luminescence of Eu/ssDNA probes initially altered by metal ions. Hence, four Eu/ssDNA-metal ion ensembles are demonstrated to be a powerful label-free TRL sensor array for pattern differentiation of eight thiols and even chiral recognition of cysteine enantiomers with different concentrations. Moreover, the sensitive TRL detection of thiols in biofluids can be successfully realized by using our method, promising its potential practical usage. This is the first report of a ssDNA-sensitized Eu-based TRL platform for label-free yet multifunctional background-free sensing and would open a door for sprouting of more novel lanthanide ion/DNA-relevant strategies toward widespread applications.

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