Zhengbo Chen

DNA-Catalytically Active Gold Nanoparticle Conjugates-Based Colorimetric Multidimensional Sensor Array for Protein Discrimination

A series of single-strand oligonucleotides functionalized catalytically active gold nanoparticle (AuNPs) as nonspecific receptors have been designed to build a protein sensing array. We take advantage of the correlation between the catalytic activity and the exposed surface area of AuNPs, i.e., DNA-proteins interactions mask the surface area of AuNPs, leading to poor catalytic performance of AuNPs. As the number of DNA-bound proteins increases, the surfaces of AuNPs become more masked; thus, the time of 4- nitrophenol/NaBH4 reaction for color change (yellow → colorless) of the solution increases. Taking advantage of three nonspecific SH-labeled DNA sequences (A15, C15, and T15) as array sensing elements and the color-change time (CCT) of the solution as signal readout, colorimetric response patterns can be obtained on the array and identified via linear discriminant analysis (LDA). Eleven proteins have been completely distinguished with 100% accuracy with the naked eye at the 30 nM level. Remarkably, two similar proteins (bovine serum albumin and human serum albumin), two different proteins (bovine serum albumin and concanavalin) at the same concentration, and the mixtures of the two proteins with different molar ratios have been discriminated with 100%. The practicability of this sensor array is further validated by high accuracy (100%) identification of 11 proteins in human serum samples.

Y-Shaped DNA Duplex Structure-Triggered Gold Nanoparticle Dimers for Ultrasensitive Colorimetric Detection of Nucleic Acid with the Dark-Field Microscope

Herein, we present a novel gold nanoparticle (AuNP) enumeration-based colorimetric aptamer biosensor for ultrasensitive detection of nucleic acid. This AuNP enumeration-based colorimetric method takes advantages of the distinctive and strong localized surface plasmon resonance light scattering with the dark-field microscope. In our model system, first, cost-effective DNA1 instead of expensive 2-thioethyl ether acetic acid was capped on the surface of AuNPs to form a dense DNA1 layer. Then, two DNA strands (DNA2 and DNA3) in two different solutions were separately asymmetrically functionalized on the AuNPs capped dense DNA1 layer. The subsequent binding of the target DNA could trigger the formation of perfect complementary DNA with a Y shape and adjust the distance between nanoparticles to form AuNP dimers, accompanied by a color change from green to yellow as observed, and thereby modulated the performance of the sensor, which resulted in the ultrahigh sensitivity. With this design, a 43 aM limit of detection was obtained, which exhibited an increase of at least 5-9 orders of magnitude in sensitivity over other colorimetric sensors fabricated using conventional strategies.

Colorimetric detection of Hg(II) by measurement the color alterations from the “before” and “after” RGB images of etched triangular silver nanoplates

AbstractIt is shown that triangular silver nanoplates (TAgNPs) are viable colorimetric probes for the fast, sensitive and selective detection of Hg(II). Detection is accomplished by reducing Hg(II) ions to elemental Hg so that an Ag/Hg amalgam is formed on the surface of the TAgNPs. This leads to the inhibition of the etching TAgNPs by chloride ions. Correspondingly, a distinct color transition can be observed that goes from yellow to brown, purple, and blue. The color alterations extracted from the red, green, and blue part of digital (RGB) images can be applied to the determination of Hg(II). The relationship between the Euclidean distances (EDs), i.e. the square roots of the sums of the squares of the ΔRGB values, vary in the 5xa0nM to 100xa0nM Hg(II) concentration range, and the limit of detection is as low as 0.35xa0nM. The color changes also allow for a visual estimation of the concentrations of Hg(II). The method is simple in that it only requires a digital camera for data acquisition and a Photoshop software for extracting RGB variations and data processing.n Graphical abstractHg2+ detection was achieved by anti-etching of TAgNPs caused by the formation of silver amalgam, along with vivid multicolor variations from yellow to brown, purple, and eventually to be blue.

Determination of nickel(II) at nanomolar levels using iodide-responsive gold-copper nanoparticles as colorimetric probes

AbstractThe authors present a colorimetric method for the quantification of Ni(II) at nanomolar levels. It is based on the use of iodide-responsive copper-gold nanoparticles (Cu-Au NPs) combined with the Ni(II)-catalyzed glutathione (GSH)-oxygen reaction system. In the presence of Ni(II), the catalytic reaction between GSH and oxygen is can triggered. This leads to the formation of GSSG which is bulky and hinders the access of iodide to the surface of the Cu-Au NPs. Concomitantly, the color of the solution containing the Cu-Au NPs changes from gray to red. Based on these findings, a method was developed for the quantitation of Ni(II) that has a detection limit as low as 0.54xa0nM. This is 1–3 orders of magnitude lower than that of previously reported optical methods. The assay has excellent selectivity for Ni(II), is rapid, cost-effective, portable, and allows for bare eye observation. Conceivably the method is suitable for field detection of Ni(II) in biological, food, and environmental samples.n Graphical AbstractA sensitive colorimetric strategy for Ni(II) through the combination of iodide-responsive Cu-Au NPs with Ni(II)-catalyzed the oxidation of GSH by oxygen was presented.

Colorimetric detection of DNA at the nanomolar level based on enzyme-induced gold nanoparticle de-aggregation

AbstractThe authors describe a colorimetric method for the determination of DNA based on the deaggregation of gold nanoparticles (AuNPs) induced by exonuclease III (Exo III). DNA amplification is accomplished by Exo III to generate large quantities of the residual DNA. Residual DNA tethers onto the surfaces of AuNPs which prevents their aggregation. Hence, the color of the solution is red. However, in the absence of DNA, salt-induced aggregation is not prevented, and the bluish-purple color of the aggregated AuNPs is observed. The ratio of absorbances at 525 and 625xa0nm increases up to 150xa0nM DNA concentrations, and the LOD is as low as 3.0xa0nM. It is shown that the presence of 300xa0nM concentrations of random DNA (with a mass up to 10-fold that of target DNA) does not interfere. The method was successfully applied to the analysis of DNA in spiked serum samples. The method is simple, reliable, and does not require complicated amplification steps and expensive instrumentation.n Graphical abstractSchematic of a sensing strategy for DNA detection by exonuclease III-inducedxa0deaggregation of gold nanoparticles. DNA concentrations asxa0 low as 3 nM can be detectedxa0via colorimetric monitoring of the color change from red to purple-blue.

Colorimetric adenosine aptasensor based on DNA cycling amplification and salt-induced aggregation of gold nanoparticles

AbstractAn aptamer based assay is described for the colorimetric detection of adenosine. The presence of adenosine triggers the deformation of hairpin DNA oligonucleotide (HP1) containing adenosine aptamer and then hybridizes another unlabeled hairpin DNA oligonucleotide (HP2). This leads to the formation of a double strand with a blunt 3′ terminal. After exonuclease III (Exo III)-assisted degradation, the guanine-rich strand (GRS) is released from HP2. Hence, the adenosine-HP1 complex is released to the solution where it can hybridize another HP2 and initiate many cycles of the digestion reaction with the assistance of Exo III. This leads to the generation of a large number of GRS strands after multiple cycles. The GRS stabilize the red AuNPs against aggregation in the presence of potassium ions. If, however, GRS forms a G-quadruplex, it loses its ability to protect gold nanoparticles (AuNPs) from salt-induced AuNP aggregation. Therefore, the color of the solution changes from red to blue which can be visually observed. This colorimetric assay has a 0.13xa0nM detection limit and a wide linear range that extends from 5xa0nM to 1xa0μM.n Graphical abstractSchematic presentation of axa0colorimetric aptamer biosensor for adenosine detection based on DNA cycling amplification and salt-induced aggregation of gold nanoparticles.

Colorimetric detection of L-histidine based on the target-triggered self-cleavage of swing-structured DNA duplex-induced aggregation of gold nanoparticles

AbstractA rapid, highly sensitive and selective colorimetric assay is presentedxa0for visually detecting L-histidine. It is based on L-histidine-triggered self-cleavage of DNA duplex-induced gold nanoparticle (AuNP) aggregation. The citrate-capped AuNPs easily aggregate in a high concentration of salt environment. However, in the presence of L-histidine aptamers (DNA1 and DNA2), the partial strands of DNA1 and DNA2 hybridize to form a DNA duplex with a swing structure. The swing-like DNA duplexes are adsorbed on the surface of AuNPs to improve the stability of AuNPs, and thexa0AuNPs also are better dispersed in high-salt media. When L-histidine is added to the solutions, it catalyzes the self-cleavage of DNA1 to form many single-stranded DNA (ssDNA) fragments. These ssDNA segments arexa0adsorbed on thexa0AuNPs and weaken the stability of AuNPs. Hence, the AuNPs aggregate in high-salt environment, and thisxa0results in a red-to-blue color change. Under the optimized conditions, L-histidine can be determinedxa0with a limit of detection of 3.6xa0nM. In addition, the sensor was successfully applied to the determination ofxa0L-histidine in spiked serum samples.n Graphical abstractSchematic of a rapid and homogeneous colorimetric L-histidine assay. It combines L-histidine-triggered self-cleavage of the swing-like DNA duplexes and self-cleavage of DNA-induced AuNP aggregation.

Colorimetric aggregation based cadmium(II) assay by using triangular silver nanoplates functionalized with 1-amino-2-naphthol-4-sulfonate

A colorimetric method is described for sensitive and low-cost detection of Cd(II). It is based on the use of triangular silver nanoplates (tri-AgNPs) modified with 1-amino-2-naphthol-4-sulfonate (ANS) acting as a colorimetric probe. ANS is first linked to the tri-AgNPs via electrostatic interaction of the sulfo groups. In the absence of analyte, ANS on the surface of tri-AgNPs protects them from aggregation. In the presence of Cd(II), the tri-AgNPs aggregate due to the interaction between ANS and Cd(II). This results in a distinct color change from blue (absorption peak at 710xa0nm) to green (peak at 770xa0nm). UV-vis spectrometry and image analyses demonstrate that this method exhibits selective and sensitive colorimetric response to Cd(II). The color change can be easily detected with bare eyes. Response is linear in the 30 to 70xa0μM concentration range, and the detection limit is 30xa0nM.Graphical abstractA colorimetric method for sensitive, and low-cost detection of Cd(II) based on the use of tri-AgNPs modified with ANS acting as a colorimetric probe was presented.

“Aggregation-to-Deaggregation” Colorimetric Signal Amplification Strategy for Ag+ Detection at the Femtomolar Level with Dark-Field Microscope Observation

Robust but ultrasensitive aptasensors with an ability to detect lower concentrations of heavy metal ions enable the detection of serious environmental and health issues. We herein develop a label-free aptasensor for ultrasensitive detection of the silver ion (Ag+) utilizing gold nanoparticle (AuNP) intensity measurement methodology by dark-field microscopy, which is based on target Ag+ and exonuclease III (Exo III)-dependent DNA cleavage recycling amplification. In the presence of target Ag+, thymine (T) bases at two termini of hairpin DNA bind with Ag+ through C-Ag+-C coordination to form a DNA duplex, Exo III can recognize the blunt 3 end of the DNA duplex and digest it from the 3 end to the 5 direction. The released target Ag+ then binds with another hairpin DNA via C-Ag+-C pairs. After many cycles of the digestion of the DNA duplex by Exo III, numerous remaining single-stranded DNA (ssDNA) are generated. These ssDNA are absorbed on the surface of AuNPs, enhancing the repulsion force between AuNPs, which further promotes the dispersion of AuNPs, leading to a significantly decreased intensity of yellow and red dots (aggregated AuNPs) under dark-field microscopy observation, in contrast to that of the blank solution (without target Ag+). On this basis, the detection limits of 41 and 39 fM were achieved for Ag+ in Tris-HCl buffer and river water, respectively.

Colorimetric Sensor Array for Discrimination of Heavy Metal Ions in Aqueous Solution Based on Three Kinds of Thiols as Receptors

In the present work, we report a novel colorimetric sensor array for rapid identification of heavy metal ions. The sensing mechanism is based on the competition between thiols and urease for binding with the metal ions. Due to the different metal ion-binding abilities between the thiols and urea, different percentages of urease are free of metal ions and become catalytically active in the presence of varied metal ions. The metal ion-free urease catalyzes the decomposition of urea releasing ammonia and changing the pH of the analyte solution. Bromothymol blue, the pH indicator, changes its color in response to the metal-caused pH change. Three different thiols (l-glutathione reduced, l-cysteine, and 2-mercaptoethanol) were used in our sensor array, leading to a unique colormetric repsonse pattern for each metal. Linear discriminant analysis (LDA) was employed to analyze the patterns and generate a clustering map for identifying 11 species of metal ions (Ni2+, Mn2+, Zn2+, Ag+, Cd2+, Fe3+, Hg2+, Cu2+, Sn4+, Co2+, and Pb2+) at 10 nM level in real samples. The method realizes the simple, fast (within 30 s), sensitive, and visual discrimination of metal ions, showing the potential applications in environmental monitoring.