Hierarchical Carbon Nanotube Membrane-Supported Gold Nanoparticles for Rapid Catalytic Reduction of <i>p</i>‑Nitrophenol

Gold nanoparticles (AuNPs) have attracted increasing attention as catalysts for pollutant degradation because of their unique reactivity. Direct use of gold nanoparticles in water treatment faces prohibitive challenges from nanoparticle aggregation and post-treatment separation. To prevent nanoparticles from aggregating and eliminate the need for separation, we affixed AuNPs on hierarchical carbon nanotube membrane (HCNM) that was approximately 50 μm thin with 10 μm × 10 μm openings as pores for water passage. HCNM was fabricated by growing vertically aligned carbon nanotube (CNT) arrays on stainless steel mesh. Using p-nitrophenol (PNP) as model pollutant, we showed that in batch experiments HCNM-supported AuNPs retained 78% of their catalytic capability compared to suspended AuNPs. The slight reduction in reactivity was attributed to the blockage of part of the gold surface at the AuNP–CNT juncture. When the membrane was used in continuous flow-through operation, HCNM-supported AuNPs achieved 71% of the maximum catalytic ability measured in batch. The rapid kinetics obtained with HCNM-supported AuNPs was in great contrast to the slow kinetics that one would expect for a rigid membrane of similar configuration. For a rigid membrane, water passing through microscopic pores was confined as laminar flow and thus would not mix well with catalysts affixed on pore walls. For HCNM, CNTs aligning pore walls were flexible so that they could move vigorously to create a chaotic mixing condition and promote AuNP-catalyzed PNP reduction

Single-molecule protein identification by sub-nanopore sensors - Fig 2

<p>(a) An example of a pore current trace acquired from a denatured H3.3 histone translocating through sub-nanopore with a nominal diameter of 0.5-nm. (b) The bottom trace is a magnified view of a 600 ms region of a top trace, showing a current blockade associated with the translocation of a single protein molecule. In the figure, higher values correspond to larger blockade currents. Blockades, associated with the translocation of single proteins were identified as regions with fluctuations five standard deviations above the noise level and with duration > 1 ms.); and then the raw current <i>I</i> was converted into <i>fractional blockade current</i>.</p

Apex-Confined Plasmonic Tip for High Resolution Tip-Enhanced Raman Spectroscopic Imaging of Carbon Nanotubes

This paper reports a handy technical scheme to decorate atomic force microscopy (AFM) tips toward tip-enhanced Raman spectroscopy (TERS) applications. The major attraction of these homemade tips lies in that silver decoration can be confined at the apex of commercial tips by the means of an AFM-controlled electrochemical reaction. The reduction of Ag+ occurs in a highly sealed environment to secure the metal coating efficiency. Key factors include silver nitrate solution to provide Ag+, ambient relative humidity and temperature in a humidity cell, electric potential bias, and tip–surface distance. Subsequently, these silver-coated tips are evaluated for TERS measurement of carbon nanotubes (CNTs) so that both morphological and chemical characteristics of CNTs are concurrently obtained. The Raman spectra reveal that our plasmonic tip competently possesses an ∼30-fold local field signal increase and the corresponding TERS image laterally resolves at the single-pixel level

Method for Dynamically Detecting Secretions from Single Cells Using a Nanopore

Secreted proteins mediate cell-to-cell communications. Thus, eavesdropping on the secretome could reveal the cellular phenotype, but it is challenging to detect the proteins because they are secreted only in minute amounts and then diluted in blood plasma or contaminated by cell culture medium or the lysate. In this pilot study, it is demonstrated that secretions from single cancer cells can be detected and dynamically analyzed through measurements of blockades in the electrolytic current due to single molecules translocating through a nanopore in a thin inorganic membrane. It is established that the distribution of blockades can be used to differentiate three different cancer cell lines (U937, MDA-MB-231, and MCF-7) in real time and quickly (<20 s). Importantly, the distinctive blockades associated with the chemokine CCL5, a prognostic factor for disease progression in breast cancer, along with other low-mass biomarkers of breast cancer (PI3, TIMP1, and MMP1) were identified in the context of the secretome of these three cell types, tracked with time, and used to provide information on the cellular phenotype

AND-Logic Cascade Rolling Circle Amplification for Optomagnetic Detection of Dual Target SARS-CoV‑2 Sequences

DNA logic operations are accurate and specific molecular strategies that are appreciated in target multiplexing and intelligent diagnostics. However, most of the reported DNA logic operation-based assays lack amplifiers prior to logic operation, resulting in detection limits at the subpicomolar to nanomolar level. Herein, a homogeneous and isothermal AND-logic cascade amplification strategy is demonstrated for optomagnetic biosensing of two different DNA inputs corresponding to a variant of concern sequence (containing spike L452R) and a highly conserved sequence from SARS-CoV-2. With an “amplifiers-before-operator” configuration, two input sequences are recognized by different padlock probes for amplification reactions, which generate amplicons used, respectively, as primers and templates for secondary amplification, achieving the AND-logic operation. Cascade amplification products can hybridize with detection probes grafted onto magnetic nanoparticles (MNPs), leading to hydrodynamic size increases and/or aggregation of MNPs. Real-time optomagnetic MNP analysis offers a detection limit of 8.6 fM with a dynamic detection range spanning more than 3 orders of magnitude. The accuracy, stability, and specificity of the system are validated by testing samples containing serum, salmon sperm, a single-nucleotide variant, and biases of the inputs. Clinical samples are tested with both quantitative reverse transcription-PCR and our approach, showing highly consistent measurement results

On-Particle Hyperbranched Rolling Circle Amplification-Scaffolded Magnetic Nanoactuator Assembly for Ferromagnetic Resonance Detection of MicroRNA

Inspired by natural molecular machines, scientists are devoted to designing nanomachines that can navigate in aqueous solutions, sense their microenvironment, actuate, and respond. Among different strategies, magnetically driven nanoactuators can easily be operated remotely in liquids and thus are valuable in biosensing. Here we report a magnetic nanoactuator swarm with rotating-magnetic-field-controlled conformational changes for reaction acceleration and target quantification. By grafting nucleic acid amplification primers, magnetic nanoparticle (MNP) actuators can assemble and be fixed with a flexible DNA scaffold generated by surface-localized hyperbranched rolling circle amplification in response to the presence of a target microRNA, osa-miR156. Net magnetic anisotropy changes of the system induced by the MNP assembly can be measured by ferromagnetic resonance spectroscopy as shifts in the resonance field. With a total assay time of ca. 120 min, the proposed biosensor offers a limit of detection of 6 fM with a dynamic detection range spanning 5 orders of magnitude. The specificity of the system is validated by testing different microRNAs and salmon sperm DNA. Endogenous microRNAs extracted from Oryza sativa leaves are tested with both quantitative reverse transcription-PCR and our approach, showing comparable performances with a Pearson correlation coefficient >0.9 (n = 20)