Ultrasensitive Automatic Detection of Small Molecules by Membrane Imaging of Single Molecule Assays

A generalizable sensing platform based on molecularly imprinted polymer-aptamer double recognition and nanoenzyme assisted photoelectrochemical-colorimetric dual-mode detection

Developing highly sensitive and selective methods that incorporate specific recognition elements is crucial for detecting small molecules because of the limited availability of small molecule antibodies and the challenges in obtaining sensitive signals. In this study, a generalizable photoelectrochemical-colorimetric dual-mode sensing platform was constructed based on the synergistic effects of a molecularly imprinted polymer (MIP)-aptamer sandwich structure and nanoenzymes. The MIP functionalized peroxidase-like Fe3O4 (Fe3O4@MIPs) and alkaline phosphatase mimic Zr-MOF labeled aptamer (Zr-mof@Apt) were used as the recognition elements. By selectively accumulating dibutyl phthalate (DBP), a small molecule target model, on Fe3O4@MIPs, the formation of Zr-MOF@Apt-DBP- Fe3O4@MIPs sandwich structure was triggered. Fe3O4@MIPs oxidized TMB to form blue-colored oxTMB. However, upon selective accumulation of DBP, the catalytic activity of Fe3O4@MIPs was inhibited, resulting in a lighter color that was detectable by the colorimetric method. Additionally, Zr-mof@Apt effectively catalyzed the hydrolysis of L-Ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAPS), generating ascorbic acid (AA) that could neutralize the photogenerated holes to decrease the photocurrent signals for PEC sensing and reduce oxTMB for colorimetric testing. The dual-mode platform showed strong linearity for different concentrations of DBP from 1.0 pM to 10 μM (PEC) and 0.1 nM to 0.5 μM (colorimetry). The detection limits were 0.263 nM (PEC) and 30.1 nM (colorimetry) (S/N = 3), respectively. The integration of dual-signal measurement mode and sandwich recognition strategy provided a sensitive and accurate platform for the detection of small molecules.

Modular Engineering of a DNA Tetrahedron-Based Nanomachine for Ultrasensitive Detection of Intracellular Bioactive Small Molecules

Bioactive small molecules serve as invaluable biomarkers for recognizing modulated organismal metabolism in correlation with numerous diseases. Therefore, sensitive and specific molecular biosensing and imaging in vitro and in vivo are particularly critical for the diagnosis and treatment of a large group of diseases. Herein, a modular DNA tetrahedron-based nanomachine was engineered for the ultrasensitive detection of intracellular small molecules. The nanomachine was composed of three self-assembled modules: an aptamer for target recognition, an entropy-driven unit for signal reporting, and a tetrahedral oligonucleotide for the transportation of the cargo (e.g., the nanomachine and fluorescent markers). Adenosine triphosphate (ATP) was used as the molecular model. Once the target ATP bonded with the aptamer module, an initiator was released from the aptamer module to activate the entropy-driven module, ultimately activating the ATP-responsive signal output and subsequent signal amplification. The performance of the nanomachine was validated by delivering it to living cells with the aid of the tetrahedral module to demonstrate the possibility of executing intracellular ATP imaging. This innovative nanomachine displays a linear response to ATP in the 1 pM to 10 nM concentration range and demonstrates high sensitivity with a low detection limit of 0.40 pM. Remarkably, our nanomachine successfully executes endogenous ATP imaging and is able to distinguish tumor cells from normal ones based on the ATP level. Overall, the proposed strategy opens up a promising avenue for bioactive small molecule-based detection/diagnostic assays.