Specific and visual assay of iodide ion in human urine via redox pretreatment using ratiometric fluorescent test paper printed with dimer DNA silver nanoclusters and carbon dots.

The fluorescence-based assay of iodide ion (I-) has been extensively studied by the use of different sensing probes and techniques, but it remains a tricky task to eliminate the interference of chloride ion (Cl-) for the analysis of low-level I- in complex genuine samples. Herein, we develop a redox pretreatment strategy for specific separating I- from human urine. Simultaneously, a novel ratiometric fluorescent probe is constructed by a simple mixing of dimer DNA silver nanoclusters (dDNA-AgNCs) and carbon dots (CDs) with the ratio of 5:1 in fluorescent intensity, and used for visual assay of I-. After addition of I-, the fluorescence of orange dDNA-AgNCs can be quenched by I- as the result of I--induced oxidative etching and aggregation of dDNA-AgNCs, while blue CDs as the stable internal standard are unresponsive to I-. With the increase of I-, the fluorescence intensity ratio (I577/I446) of binary-color probe gradually decreased, which leads to color variation from salmon pink to lighter salmon pink to lilac to light steel blue to final deep sky blue (under a UV lamp) with a sensitive detection limit of 19.8 nM. The assay for I- can also be convenient to implement for visual monitoring of I- by observing color change of test paper printed with the ratiometric probe, responding to 50 nM that is about 1 order of magnitude lower than the median urinary I- concentration defined by the World Health Organization (WHO) for school-age children. The sensitive test paper can provide an advanced platform for colorimetric and visual monitoring of I- in human urine.

Base amount-dependent fluorescence enhancement for the assay of vascular endothelial growth factor 165 in human serum using hairpin DNA-silver nanoclusters and oxidized carbon nanoparticles.

A base amount-dependent fluorescence enhancement-based strategy is put forward to determine vascular endothelial growth factor 165 (VEGF165) in human serum by the use of hairpin DNA-silver nanoclusters (hDNA-AgNCs) and oxidized carbon nanoparticles (CNPs). The hDNA-AgNCs aptasensing probe consists of AgNCs-contained hairpin loop (that generates a fluorescence signal), hairpin stem (that makes the structure stable), and the terminal aptamer 1 (that recognizes the target together with aptamer 2). It has been demonstrated that the fluorescence intensity of hDNA-AgNCs is ~ 3-fold stronger than that of single-stranded DNA-AgNCs (ssDNA-AgNCs), and hDNA-AgNCs have a strong dependence of fluorescence enhancement on the base amount in hairpin stem and loop. Upon the addition of oxidized CNPs, the terminal aptamer 1 of hDNA-AgNCs can adsorb onto the surface of oxidized CNPs via π-π stacking, and the fluorescence of hDNA-AgNCs (with excitation/emission maxima at 490/567 nm) is quenched via fluorescence resonance energy transfer (FRET). When aptamer 2 and VEGF165 are subsequently added, aptamer 1, VEGF165, and aptamer 2 reassemble into an intact tertiary structure, and the fluorescence is recovered because hDNA-AgNCs are far away from the surface of oxidized CNPs and the FRET efficiency decreases. Under the optimized conditions, the aptasensing probe can selectively assay VEGF165 with a detection limit of 14 pM. The results provide a label-free and sensitive method to monitor VEGF165 in human serum. Schematic representation of the strong dependence of fluorescence enhancement on base amount in stem and loop of hairpin DNA-silver nanoclusters. The probe can be used to assay vascular endothelial growth factor 165 (VEGF165) and give a judgment whether human serum VEGF165 is at a normal or abnormal level for clinical diagnosis.

Salt-induced gold nanoparticles aggregation lights up fluorescence of DNA-silver nanoclusters to monitor dual cancer markers carcinoembryonic antigen and carbohydrate antigen 125.

In clinical diagnosis of cancer, the monitoring of single tumor marker may result in many false and missed results, while simultaneous detection of multiple tumor markers should be more accuracy and effective. Here, we report a new strategy that salt-induced gold nanoparticles (AuNPs) aggregation lights up fluorescence of dual-color DNA-silver nanoclusters-aptamer (DNA-AgNCs-apta) for the simultaneous monitoring of carcinoembryonic antigen (CEA) and carbohydrate antigen 125 (CA125). The dual-color aptasensor system is composed of green-emitting DNA-AgNCs with CEA aptamer (gDNA1-AgNCs-apta1) and red-emitting DNA-AgNCs with CA125 aptamer (rDNA2-AgNCs-apta2) in the ratio of 1:1 in volume. Upon addition of AuNPs, gDNA1-AgNCs-apta1 and/or rDNA2-AgNCs-apta2 are flexibly adsorbed onto the surface of AuNPs by terminal aptamer(s), which prevents salt-induced AuNPs aggregation under high salt condition and results in fluorescence quenching based on surface plasmon enhanced energy transfer (SPEET). With the addition of CEA and/or CA125, the target(s) and corresponding aptamer(s) coordinate to form the complex, keeping DNA-AgNCs-apta(s) far away from the surface of AuNPs and making AuNPs aggregated in high salt medium. The AuNPs aggregation leads to the recovery of fluorescence signals of DNA-AgNCs-apta(s) due to weakened SPEET. Utilizing the fluorescence aptasensor system, the limit of detection of CEA and CA125 are as low as 7.5 pg·mL-1 and 0.015 U·mL-1, respectively. The proposed method can be applied to the selective and simultaneous determination of CEA and CA125 in human serum.

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.