Melamine detection in milk and other foods has attracted much attention since the discovery that melamine-adulterated food causes severe kidney damage. Although many methods have been developed to detect melamine, few methods can provide quantitative results using an affordable and portable device that is suitable for home use or field application. To achieve this goal, we herein report the first in vitro selection of a melamine responsive aptamer using a structure-switching method. A personal glucose meter (PGM) based melamine sensor was designed and subsequently tested using the newly isolated aptamer. Conversion of melamine concentration to glucose amount was achieved by including an invertase-conjugated DNA that is complementary to part of the aptamer. Melamine binding triggers the release of the invertase-DNA conjugate, which hydrolyzes sucrose into glucose. The glucose produced is then measured directly using an off-the-shelf PGM. The described sensor shows high selectivity for melamine against several closely related melamine analogues, such as cyanuric acid, ammeline, and ammelide, and has low detection limits of 0.33 μM (or 41.1 ppb) in buffer and 0.53 μM (or 67.5 ppb) in 80% whole milk without any pretreatment. The detection limits meet the threshold of 2.5 ppm for non-infant-formula products and 1 ppm for melamine in infant milk products as defined by the U.S. Food and Drug Administration (FDA). In addition to the PGM sensor demonstrated here, the same aptamer can be converted into other types of sensors with different signal outputs, allowing portable detection of melamine under a variety of conditions.

RNA-cleaving DNAzymes are useful tools for intracellular metal-ion sensing and gene regulation. Incorporating stimuli-responsive modifications into these DNAzymes enables their activities to be spatiotemporally and chemically controlled for more precise applications.Despite the successful development of many caged DNAzymes for light-induced activation, DNAzymes that can be intracellularly activated by chemical inputs of biological importance,s uch as reactive oxygen species (ROS), are still scarce.R OS like hydrogen peroxide( H 2 O 2 )a nd hypochlorite (HClO) are critical mediators of oxidative stress-related cell signaling and dysregulation including activation of immune system as well as progression of diseases and aging.H erein, we report ROS-activable DNAzymes by introducing phenylboronate and phosphorothioate modifications to the Zn 2+ -dependent 8-17 DNAzyme. These ROS-activable DNAzymes were orthogonally activated by H 2 O 2 and HClO inside live human and mouse cells.

No abstract

No abstract

This study demonstrates the use of carrier-protein/haptens conjugate (e.g., BSA/2,4-dichlorophenoxyacetic acid, 2,4-D-BSA) for biological modification of quantum dots (QDs) for the detection of small analytes. Bioconjugated QDs, which are used as a detection nanoimmunoprobe, were prepared through conjugating carboxyl QDs with 2,4-D-BSA conjugate. Based on the principle of quantum dot-fluorescence resonance energy transfer (QD-FRET), an all-fiber microfluidic biosensing platform has been developed for investigating FRET efficiency, immunoassay mechanism and format, and binding kinetics between QD immunoprobe and fluorescence labeled anti-2,4-D monoclonal antibody. The structure of multiplex-haptens/BSA conjugate coupling to QD greatly improves the FRET efficiency and the sensitivity of the nanosensor. With a competitive detection mode, samples containing different concentrations of 2,4-D were incubated with a given concentration of QD immunoprobe and fluorescence-labeled antibody, and then detected by the all-fiber microfluidic biosensing platform. A higher concentration of 2,4-D led to less fluorescence-labeled anti-2,4-D antibody bound to the QD immunoprobe surface and, thus, a lower fluorescence signal. The quantification of 2,4-D over concentration ranges from 0.5 nM to 3 μM with a detection limit determined as 0.5 nM. The performance of the nanosensor with spiked real water samples showed good recovery, precision, and accuracy, indicating that it was less suspectable to water matrix effects. With the use of different QD nanobioprobes modified by other carrier-protein/haptens conjugates, this biosensing protocol based on QD-FRET can be potentially applied for on-site, real-time, inexpensive, and easy-to-use monitoring of other trace analytes.