We present a new method for specific detection of oxytetracycline (OTC) at nanomolar concentrations based on a microfabricated cantilever array. The sensing cantilevers in the array are functionalized with self-assembled monolayers (SAMs) of OTC-specific aptamer, which acts as a recognition molecule for OTC. While the reference cantilevers in the array are functionalized with 6-mercapto-1-hexanol SAMs to eliminate the influence of environmental disturbances. The cantilever sensor shows a good linear relationship between the deflection amplitude and the OTC concentration in the range of 1.0–100 nM. The detection limit of the cantilever array sensor is as low as 0.2 nM, which is comparable to some traditional methods. Other antibiotics such as doxycycline and tetracycline do not cause significant deflection of the cantilevers. It is demonstrated that the cantilever array sensors can be used as a powerful tool to detect drugs with high sensitivity and selectivity.

We report a simple and sensitive method for label-free detection of single-stranded DNA-binding protein (SSBP) based on an array of microfabricated cantilevers. The single-stranded DNA (ssDNA) was immobilized on the surface of the sensing cantilevers to detect SSBP, while the reference cantilevers were modified with 6-mercapto-1-hexanol to detect any unwanted cantilever deflection. The differential deflection signals that reveal specific SSBP–ssDNA binding have been found to depend on the SSBP concentration. Using the cantilever array sensor we can detect SSBP in the concentration range from 0.01 to 7 μg mL−1. Other proteins, such as thrombin or bovine serum albumin induced no significant deflection of the cantilevers. Our results show the potential for the application of cantilever array sensor system as a powerful tool to detect proteins with high sensitivity and specificity.Highlights► A novel cantilever array sensor for single-stranded DNA-binding protein (SSBP) detection was developed. ► No need for labeling procedures. ► Low detection limit was obtained. ► The sensor shows good selectivity to SSBP.

The luteinizing hormone-releasing hormone-Pseudomonas aeruginosa exotoxin 40 (LHRH-PE40), is a candidate target drug associated with elevated LHRH receptor (LHRH-R) expression in malignant tumor tissue. The capability of LHRH-PE40 to recognize LHRH-Rs on a living cell membrane was studied with single molecular recognition force spectroscopy (SMFS) based on atomic force microscopy (AFM). The recognition force of LHRH-PE40/LHRH-R was compared with that of LHRH/LHRH-R by dynamic force spectroscopy. Meanwhile, cell growth inhibition assay and fluorescence imaging were presented as complementary characterization. The results show that LHRH moiety keeps its capability to recognize LHRH-R specifically, which implies that recombinant protein LHRH-PE40 can be a promising target drug.

The self-assembled structures possess superior stability, biocompatibility and mechanical strength, and their study can provide insight into the use of creating novel biomaterials. Atomic force microscopy (AFM) images of single-stranded DNA (ssDNA) nanostructures show that well-ordered organization, high homogeneity, and molecular dimensions fractal-shaped fibers formed on a gold substrate covered with self-assembled monolayers (SAMs) of 1-hexadecanethiol (HDT). The nanoscaled architectures of ssDNA on HDT/Au changed remarkably following the process of diffusion-limited cluster aggregation (DLA) over time. The ssDNA fibers prefer to form on hydrophobic SAMs instead of hydrophilic SAMs, and the ssDNA has to have complementary regions in their sequences. This method might not be used only for the construction of fractal patterns, but also for the design and fabrication of functional DNA-based, self-assembled materials that exhibit self-similarity at multiple length scales.

Nanoelectrochemical patterning of 1-hexadecanethiol (HDT) monolayer on Au(111) was realized by thiol-modified conductive atomic force microscopy (AFM) tips in a fashion of mild oxidation of top methyl groups of the monolayers. Pt-coated tips modified by a hydrophobic and appropriate thick monolayer of thiol (e.g., HDT) can significantly increase the bias threshold and extend the bias range suitable for the constructive nanolithography (CNL) in comparison with those tips unmodified or modified by hydrophilic monolayers. Furthermore, the switchover from the CNL to the deep oxidation can be governed by the reductive desorption of thiol monolayers from the tip surface when appropriate thiol-modified tips are used. A hydrophobic HDT/tip can exhibit a CNL bias range with an extent of 5.3 V, much wider than the reported extents of the CNL bias ranges on octadecyl trichlorosilane (OTS)/silicon surfaces by unmodified tips. The resulting CNL patterns were shown to have potential as multifunctional templates by guiding the self-assembly of OTS and the site-defined immobilization of aminopropyltriethoxysilane-modified α-Fe2O3 nanoparticles.

The adsorption of dopamine (DA) molecules on gold and their interactions with Fe3+ were studied by a microcantilever in a flow cell. The microcantilever bent toward the Au side with the adsorption of DA due to the change of surface stress induced by the intermolecular hydrogen bonds of DA or the charge transfer effect between adsorbates and the substrate. The interaction process between DA adsorbates and Fe3+ was revealed by the deflection curves of microcantilever. As indicated by the appearance of a variation during the decline of curves, two steps were observed in the curve at relative high concentrations of Fe3+. In this case, Fe3+ reacted with DA molecules only in the outer layers and the complexes removed with solution. Then Fe3+ reacted further with DA molecules forming the surface complex in the first layer next to the gold. At this stage, the stability of surface complexes was time dependent, i.e., unstable initially and stable finally. This may be due to the surface complexes change from mono-dentate to bi-dentate complexes. In another case, i.e., at relative low concentration of Fe3+, only the first step was observed as indicated by the absence of a variation. X-ray photoelectron spectroscopy (XPS) and cycling voltammetry (CV) results provided complementary evidence for the result of microcantilever and proposal. As low as 5 × 10−10 M Fe3+ was detected by DA modified microcantilever with a good selectivity over other common metal ions.

The replacement of coronene monolayer on Au (111) by 6-mercapto-1-hexanol (MHO) was studied by in situ scanning tunneling microscopy (STM) in solutions. It was found that the rate of replacement depends strongly on the concentration of MHO. The replacement finished within a second at a higher concentration of MHO. At a lower concentration, the slow replacement could be followed by in situ STM. The replacement occurred initially near the elbow position of reconstructed Au (111) with the formation of pits in a single or several missing molecules. With the proceeding of replacement, these small pits expanded, and the surrounding coronene molecules were gradually substituted by MHO, which developed into ordered domains within a spatial confined environment. Meanwhile, the reconstruction of Au (111) was lifted. The replacement expanded fast along the reconstruction lines in the domain. For the fast replacement, a (√3 × √3) R30° adlattice was observed, while a c(4 × 2) superlattice was observed for the slow replacement. The close-packed phase of MHO self-assembled monolayers (SAMs) appeared directly instead of a flat-lying phase, which implied that the coronene molecules resist the direct contact of hydrocarbon chain of MHO with Au (111) surface. The replacing rate of the overall process exhibited a signoidal shape with time.

Carbohydrates are involved in many essential biological recognition processes in physiological and pathological states. Thus, it is important to understand the mechanism of protein–carbohydrate interactions at molecular level. In the present study, molecular recognition force spectroscopy was applied to investigate the interactions between RCA120, a lectin from Ricinus communis, and galactose (Gal) and asialofetuin (ASF) at the single-molecule level. RCA120 coupled to the AFM tip could specifically recognize Gal and ASF, respectively. The unbinding forces of RCA120–Gal and RCA120–ASF increase linearly with the logarithm of loading rate. The results reveal that the binding capability of RCA120 toward Gal is weaker than that of ASF, implicating a multivalent effect in the RCA120–ASF interaction.