Ratiometric fluorescent test pen filled with a mixing ink of carbon dots and CdTe quantum dots for portable assay of silver ion on paper.

A ratiometric fluorescent test pen filled with a mixing ink of blue carbon dots (CDs) and red CdTe quantum dots (CdTe QDs) is introduced for portable assay of silver ion (Ag(I)) on paper. The mixing ink was tuned with ratiometric fluorescent intensity of 1:5, and then filled into a vacant commercial fluorescent pen core. Writing/painting a random word/figure on a blank paper can make the most portable nanoprobe determining Ag(I) by visualization. Ag(I) can adsorb onto the surface of CdTe QDs, which leads to the formation of surficial Ag2Te layer by an ion-exchanging reaction. This enables the red fluorescence of CdTe QDs (with excitation/emission maxima at 360/628 nm) to be quenched. Due to the unchanged blue fluorescence of CDs (with excitation/emission maxima at 360/440 nm) as internal standard, the solution color evolves gradually from red to blue with the increase of Ag(I) concentration with a detection limit of 3.48 nM. This is at least 2 orders of magnitude lower than the limit defined by World Health Organization (WHO) in drinkable water. The fluorescent test pen has also been used for the determination of Ag(I) in wastewater. Graphical abstract Ag(I) can adsorb on the surface of CdTe QDs to quench their fluorescence, while the fluorescent intensity of CDs keep constant, accompanying color change with the increase of Ag(I) concentration. The method offers a visual assay of Ag(I) in water.

A chemometric modeling-free near infrared barcode strategy for smart authentication and geographical origin discrimination of Chinese ginseng.

With the growing interest in alternative medicine, handy identification and differentiation of herbal medicines are becoming increasingly important. Here we report a chemometric modeling-free near infrared (NIR) barcode strategy for the smart identification and geographical origin discrimination of Chinese ginseng. The novel strategy demands the transformation of Chinese ginseng (standard and sample) NIR spectra into a barcode representation through assigning zero intensity to every NIR peak except the peaks having intensities greater than average peak intensity. Meanwhile, for Chinese ginseng standard NIR barcode, barcoding condition such as padding size was carefully optimized. It has been demonstrated that the padding size for each bar in the barcode is 8 cm-1. By comparing the percentage of nonzero overlap between Chinese ginseng standard barcode and sample barcodes, eight batches of samples (including Chinese ginseng, American ginseng and counterfeit) were successfully identified with 100% accuracy, respectively. Interestingly, the discrimination of the origin of ginsengs from three provinces (Jilin, Liaoning and Heilongjiang) of Northeastern China was achieved utilizing NIR barcode method. Two characteristic bars at 7750 and 8250 cm-1 were inspected in the ginseng sample from Jilin province, two specific bars at 6780 and 7015 cm-1 were displayed in the ginseng sample from Liaoning province and three distinct bars at 6560, 6910 and 7995 cm-1 were monitored in the ginseng sample from Heilongjiang province. The results indicate that the proposed method will be greatly expanded and applied as an inspecting platform for the on-site analysis and valid identification of Chinese ginseng in herbal markets by a handheld spectrometer or barcode scanner.

A split aptamer-labeled ratiometric fluorescent biosensor for specific detection of adenosine in human urine.

A dual-emission ratiometric fluorometric aptasensor is presented for highly specific detection of adenosine. An adenosine binding aptamer (ABA) was split into two halves (termed as ABA1 and ABA2). ABA1 was covalently bound to blue-emitting carbon dots (with excitation/emission maxima at 365/440 nm) as responsive fluorophore (referred to as ABA1-CDs). ABA2 was linked to red-emitting silica-coated CdTe quantum dots (with excitation/emission maxima at 365/613 nm) acting as internal reference and referred to as ABA2-QDs@SiO2. Upon addition of graphene oxide, the fluorescence of ABA1-CDs is quenched. After subsequent addition of ABA2-QDs@SiO2 and different amounts of adenosine, the blue fluorescence is recovered and causes a color change from red to royal blue. The method represents a ratiometric turn-on assay for visual, colorimetric and fluorometric determination of adenosine. The limit of detection is as low as 2.4 nM in case of ratiometric fluorometry. The method was successfully applied to the determination of adenosine in (spiked) human urine. Recoveries range from 98.8% to 102%. Graphical abstract Adenosine binding aptamer1-carbon dots (ABA1-CDs) can absorb on graphene oxide (GO) via π stacking. This causes fluorescence to be quenched by fluorescence resonance energy transfer (FRET). After addition of ABA2-silica-coated quantum dots (ABA2-QDs@SiO2) and adenosine, binding of adenosine to two pieces of aptamers forms a complex (ABA1-CD/adenosine/ABA2-QD@SiO2) which dissociates from GO. As a result, fluorescence is recovered.

Toward rapid analysis, forecast and discovery of bioactive compounds from herbs by jointly using thin layer chromatography and ratiometric surface-enhanced Raman spectroscopy technique.

Conventional isolation and identification of active compounds from herbs have been extensively reported by using various chromatographic and spectroscopic techniques. However, how to quickly discover new bioactive ingredients from natural sources still remains a challenging task due to the interference of their similar structures or matrices. Here, we present a grand approach for rapid analysis, forecast and discovery of bioactive compounds from herbs based on a hyphenated strategy of thin layer chromatography and ratiometric surface-enhanced Raman spectroscopy. The performance of the hyphenated strategy is first evaluated by analyzing four protoberberine alkaloids, berberine (BER), coptisine (COP), palmatine (PAT) and jatrorrhizine (JAT), from a typical herb Coptidis Rhizoma as an example. It has been demonstrated that this coupling method can identify the four compounds by characteristic peaks at 728, 708, 736 and 732 cm-1, and especially discriminate BER and COP (with similar migration distances) by ratiometric Raman intensity (I708/I728). The corresponding limits of detection are 0.1, 0.05, 0.1 and 0.5 µM, respectively, which are about 1-2 orders of magnitude lower than those of direct observation method under 254 nm UV lamp. Based on these findings, the proposed method further guides forecast and discovery of unknown compounds from traditional Chinese herb Typhonii Rhizoma. Results infer that two trace alkaloids (BER and COP) from the n-butanol extract of Typhonii Rhizoma are found for the first time. Moreover, in vitro experiments manifest that BER can effectively decrease the viability of human glioma U87 cells by inducing cell cycle arrest in a concentration-dependent manner.

Profuse color-evolution-based fluorescent test paper sensor for rapid and visual monitoring of endogenous Cu2+ in human urine.

The fluorescent paper for colorimetric detection of metal ions has been widely fabricated using various sensing probes, but it still remains an elusive task to design a test paper with multicolor variation with target dosages for accurate determination. Herein, we report a profuse color-evolution-based fluorescent test paper sensor for rapid and visual monitoring of Cu2+ in human urine by printing tricolor probe onto filter paper. The tricolor probe consists of blue-emission carbon dots (bCDs), green-emission quantum dots (gQDs) and red-emission quantum dots (rQDs), which is based on the principle that the fluorescence of gQDs and rQDs are simultaneously quenched by Cu2+, whereas the bCDs as the photostable internal standard is insensitive to Cu2+. Upon the addition of different amounts of Cu2+, the ratiometric fluorescence intensity of the tricolor probe continuously varied, leading to color changes from shallow pink to blue with a detection limit of 1.3nM. When the tricolor probe solution was printed onto a sheet of filter paper, as-obtained test paper displayed a more profuse color evolution from shallow pink to light salmon to dark orange to olive drab to dark olive green to slate blue to royal blue and to final dark blue with the increase of Cu2+ concentration compared with dual-color probe-based test paper, and dosage scale as low as 6.0nM was clearly discriminated. The sensing test paper is simple, rapid and inexpensive, and serves as a visual platform for ultrasensitive monitoring of endogenous Cu2+ in human urine.

Ehrlich Reaction Evoked Multiple Spectral Resonances and Gold Nanoparticle Hotspots for Raman Detection of Plant Hormone.

Surface-enhanced Raman scattering (SERS) by use of noble metal nanoparticles has become a powerful tool to determine a low-concentration target by unique spectral fingerprints, but it is still limited to the Raman-inactive and nonresonant biomolecules such as amine acids, proteins, and hormones. Here, we report an Ehrlich reaction based derivative strategy in combination with gold nanoparticles (Au NPs) hotspots for the selective detection of indole-like plant hormones by SERS spectroscopy. Ehrlich reaction of p-(dimethylamino)benzaldehyde (PDAB) with the indole ring chemically transformed plant hormone indole-3-butyric acid (IBA) into a Raman-active and resonant derivative with an extended π-conjugated system in the form of a cation, which produced a new absorption band at 626 nm. On the other hand, cationic IBA-PDAB highly evoked the aggregation of Au NPs with negative citrate ligands to form the effective Raman hotspots and gave rise to the new absorption ranging from 600 to 800 nm. Significantly, the spectral overlap among IBA-PDAB, aggregated Au NPs, and the exciting laser initiated the multiple optical resonances to generate the ultrahigh Raman scattering with a sensitive limit of 2.0 nM IBA. The IBA in the whole sprouts and various parts of pea, mungbean, soybean, and black bean has been identified and quantified. The reported method opens a novel avenue for the SERS detection of Raman-inactive analyte by a proper derivation.