There is an increasing interest in the development of surface-enhanced Raman scattering (SERS) sensors for rapid and accurate on-site detection of hidden explosives. However, portable SERS methods for trace explosive detection in real systems remain scarce, mainly due to their relatively poor reliability and portability. Herein, we present the first demonstration of a portable silicon-based SERS analytical platform for signal-on detection of trace trinitrotoluene (TNT) explosives, which is made of silver nanoparticle (AgNP)-decorated silicon wafer chip (0.5 cm × 0.5 cm). In principle, under 514 nm excitation, the Raman signals of p-aminobenzenethiol (PABT) modified on the AgNP surface could be largely lit up due to the formation of electronic resonance-active TNT-PABT complex. In addition, the surface of AgNPs and silicon substrate-induced plasmon resonances also contribute the total SERS enhancement. For quantitative evaluation, the as-prepared chip features ultrahigh sensitivity [limit of detection is down to ∼1 pM (∼45.4 fg/cm)] and adaptable reproducibility (relative standard deviation is less than 15%) in the detection of TNT standard solutions. More importantly, the developed chip can couple well with a hand-held Raman spectroscopic device using 785 nm excitation, suitable for qualitative analysis of trace TNT even at ∼10 M level from environmental samples including lake water, soil, envelope, and liquor with a short data acquisition time (∼1 min). Furthermore, TNT vapors diffusing from TNT residues (∼10 M) can be detected by using such a portable device, indicating its feasibility in determination of hidden samples.

There are only a few systematic rules about how to selectively control the formation of DNA-templated metal nanoparticles (NPs) by varying sequence combinations of double-stranded DNA (dsDNA), although many attempts have been made. Herein, we develop a facile method for sequence-dependent formation of fluorescent CuNPs by using dsDNA as templates. Compared with random sequences, AT sequences are better templates for highly fluorescent CuNPs. Other specific sequences, for example, GC sequences, do not induce the formation of CuNPs. These results shed light on directed DNA metallization in a sequence-specific manner. Significantly, both the fluorescence intensity and the fluorescence lifetime of CuNPs can be tuned by the length or the sequence of dsDNA. In order to demonstrate the promising practicality of our findings, a sensitive and label-free fluorescence nuclease assay is proposed.

Lead ions (Pb) and mercury ions (Hg), the two commonly coexisting heavy metal ions, pose severe risks to environment and human health. To date, no surface-enhanced Raman scattering (SERS) sensor has been reported for the simultaneous quantification of Pb and Hg in real systems. Herein, the first demonstration of SERS chips for simultaneous quantification of Pb and Hg in real systems is presented based on the combination of reproducible silicon nanohybrid substrates and a corrective internal standard (IS) sensing strategy. This chip was made of a silver nanoparticle-decorated silicon wafer via modification of the IS, i.e. 4-aminothiophenol, molecules. The as-prepared chip was further functionalized with Pb- and Hg- specific DNA strands capable of simultaneously detecting Pb and Hg. Quantitatively, upon correction by the IS Raman signals, the broad dynamic ranges from 100 pM to 10 μM for Pb and from 1 nM to 10 μM for Hg were achieved, with the detection limit down to 19.8 ppt for Pb and 168 ppt for Hg. For real applications, we further demonstrated that Pb and Hg spiked into industrial wastewater could be readily distinguished via the presented chip, and the relative standard deviation (RSD) value was less than ∼15%. More significantly, the resulting SERS chip can be well coupled with a hand-held Raman instrument and can then be used for the qualitative analysis of both Pb and Hg in real systems in a portable manner. Our results suggest that this high-quality SERS chip is a powerful tool for on-site detection of various heavy metal ions in real samples in the field of food safety and environment protection.

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It is of great significance to accurately and reliably detect trace lead(II) (Pb(2+)) ions, preferably at sub-nM level due to the possible long-term accumulation of Pb(2+) in the human body, which may cause serious threats to human health. However, a suitable Pb(2+) sensor meeting the demands is still scanty. Herein, we develop a polyadenine-assisted, surface-enhanced Raman scattering (SERS) silicon chip (0.5 cm × 0.5 cm) composed of core (Ag)-satellite (Au) nanoparticles (Ag-Au NPs)-decorated silicon wafers (Ag-Au NPs@Si) for high-performance Pb(2+) detection. Typically, strong SERS signals could be measured when DNAzyme conjugated on the SERS silicon chip is specifically activated by Pb(2+), cleaving the substrate strand into two free DNA strands. A good linearity exists between the normalized Raman intensities and the logarithmic concentrations of Pb(2+) ranging from 10 pM to 1 μM with a good correlation coefficient, R(2) of 0.997. Remarkably, Pb(2+) ions with a low concentration of 8.9 × 10(-12) M can be readily determined via the SERS silicon chip ascribed to its superior SERS enhancement, much lower than those (∼nM) reported by other SERS sensors. Additionally, the developed chip features good selectivity and recyclability (e.g., ∼11.1% loss of Raman intensity after three cycles). More importantly, the as-prepared chip can be used for accurate and reliable determination of unknown Pb(2+) ions in real systems including lake water, tap water and industrial wastewater, with the RSD value less than 12%.