•A sensitive sensor for hemoglobin detection down to subnanomolar was developed.•Hydrogen peroxide quenched the fluorescence from protein-stabilized gold nanoclusters.•Hemoglobin significantly enhanced this quenching at even a low concentration.•The applicability of the sensor was validated with blood sample analyses.In this report, a fluorescence sensor for sensitive detection of hemoglobin was developed. Gold nanoclusters were first synthesized with bovine serum albumin. It was found that both hydrogen peroxide and hemoglobin could weakly quench the fluorescence from the gold nanoclusters, but when these two were applied onto the nanolcusters simultaneously, a much improved quenching was resulted. This enhancing effect was proved to come from the catalytic generation of hydroxyl radical by hemoglobin. Under an optimized condition, the quenching linearly related to the concentration of hemoglobin in the range of 1–250 nM, and a limit of detection as low as 0.36 nM could be obtained. This provided a sensitive means for the quantification of Hb. The sensor was then successfully applied for blood analyses with simple sample pretreatment.Download high-res image (198KB)Download full-size image

•Iodine together with iodide etched the metallic core of gold nanoclusters and brought in fluorescence quenching.•Ascorbic acid reduced iodine into iodide and inhibited related quenching.•A "turn-on" fluorescence detection of ascorbic acid down to 22 nM was obtained.In this report, a sensitive fluorescent detection of ascorbic acid was developed with protein-stabilized gold nanoclusters. The fluorescence signal from the gold nanoclusters could be effectively quenched by elemental iodine. This kind of quenching could be inhibited by ascorbic acid through a corresponding reduction process, thus a turn-on response toward ascorbic acid was obtained. The validity and performances of the detection scheme were evaluated. The fluorescence responses were linearly related to ascorbic acid in the concentration range 0.1–10 μM, and the method was capable of detecting ascorbic acid down to 22 nM. The high performances of the developed scheme greatly simplified the sample preparation step, and the method was successfully applied for real sample analyses.

•Hydrogen peroxide quenched fluorescence from gold nanolcuster.•Iodide enhanced the quenching effect.•Urate oxidase was applied for the degradation of uric acid and generation of hydrogen peroxide.•A selective sensor toward uric acid with LOD as 120 nM was developed.In this report, we developed a highly sensitive and selective sensor for the detection of uric acid. Gold nanoclusters were synthesized with bovine serum albumin as the template material. Under the catalysis of urate oxidase, hydrogen peroxide was generated, which quenched the fluorescence from the gold nanoclusters. Furthermore, excessive iodide was found capable of enhancing this quenching effect, which significantly improved the sensitivity of the detection. Under an optimized condition, the extent of quenching was found linearly related to uric acid concentration in the range of 0.7–80 μM, and uric acid as low as 120 nM could be detected. With simple dilutions, blood samples could be analyzed, and satisfactory recoveries were obtained.

•BSA-stabilized gold nanoclusters were synthesized.•Iodate etched the gold core of nanocluster and resulted in fluorescence quenching.•Excessive iodide enhanced the etching and related quenching.•A highly sensitive iodate sensor was developed.In this report we described a highly selective and sensitive iodate sensor. Due to its interaction with fluorescent gold nanoclusters, iodate was capable of oxidizing and etching gold core of the nanoclusters, resulting in fluorescence quenching. Furthermore, it was found that extra iodide ion could enhance this etching process, and even a small amount of iodate could lead to significant quenching. Under an optimized condition, linear relationship between the iodate concentration and the fluorescence quenching was obtained in the range 10 nM–1 μM. The developed iodate sensor was found selective and capable of detecting iodate as low as 2.8 nM. The sensor was then applied for the analysis of iodate in real sample and satisfactory recoveries were obtained.

In this report, we have developed a method that improved the selectivity of gold nanoclusters toward copper and mercury ions. Bovine serum albumin stabilized gold nanocluster responded to both these two ions through fluorescence quenching. EDTA and sodium borohydride were added respectively as the “masking” reagents, in which EDTA complexed with Cu2+, and borohydride reduced Hg2+ into Hg0. Both these reactions inhibited the ions' interaction with the nanocluster and eliminated related quenching effect, thus detection of the other ion was achieved. Good selectivity of the nanocluster over these two ions was obtained enabling sensitive detection even under their coexistence.Highlights► Borohydride reduces mercury ion. ► EDTA complexes with copper ion. ► Masks quenching effect onto gold nanocluster respectively. ► Improves selectivity and eliminates interferences.

In this work, novel biosensing systems were developed for DNAzyme-based assays in homogenous aqueous media. The two halves of a horseradish peroxidase mimicking DNAzyme were assembled onto different gold nanoparticle surfaces through hybridization with corresponding linking DNA sequences. In the analyses, the target molecules were recognized by the linking DNA. This recognition broke the hybridization and released the DNAzyme halves from the nanoparticle surface into the solution. Together, both the DNAzyme halves combined with a cofactor hemin and turned into a catalytic hemin/G-quadruplex structure, which amplified the luminol oxidation for a turn-on chemiluminescence signaling. Based on this nanoparticle-based DNAzyme-halves design, only low background noise showed up within the homogenous solution and no separation was required in the detection steps. Aptasensor and DNA sensor were developed and analyses of the target molecules adenosine and target DNA were achieved down to 0.7 μM and 0.3 nM respectively with satisfactory selectivity.Highlights► Two DNAzyme halves are assembled onto different gold nanoparticles. ► Recognition of the target molecule releases both of DNAzyme halves and turns on catalysis together with a cofactor hemin. ► Amplifies luminol chemiluminescence as signaling. ► Analyses in homogenous media without separation.