High Sensitivity Near-Infrared Imaging of Fluorescent Nanosensors

Biochemical processes are fast and occur on small-length scales, which makes them difficult to measure. Optical nanosensors based on single-wall carbon nanotubes (SWCNTs) are able to capture such dynamics. They fluoresce in the near-infrared (NIR, 850–1700 nm) tissue transparency window and the emission wavelength depends on their chirality. However, NIR imaging requires specialized indium gallium arsenide (InGaAs) cameras with a typically low resolution because the quantum yield of normal Si-based cameras rapidly decreases in the NIR. Here, an efficient one-step phase separation approach to isolate monochiral (6,4)-SWCNTs (880 nm emission) from mixed SWCNT samples is developed. It enables imaging them in the NIR with high-resolution standard Si-based cameras (>50× more pixels). (6,4)-SWCNTs modified with (GT)₁₀-ssDNA become highly sensitive to the important neurotransmitter dopamine. These sensors are 1.7× brighter and 7.5× more sensitive and allow fast imaging (<50 ms). They enable high-resolution imaging of dopamine release from cells. Thus, the assembly of biosensors from (6,4)-SWCNTs combines the advantages of nanosensors working in the NIR with the sensitivity of (Si-based) cameras and enables broad usage of these nanomaterials.     

Geometrically Structured Nanomaterials for Nanosensors,NEMS, and Nanosieves

Recently, geometrically structured nanomaterials have received great attention due to their unique physical and chemical properties, which originate from the geometric variation in such materials. Indeed, the use of various geometrically structured nanomaterials has been actively reported in enhanced-performance devices in a wide range of applications. Recent significant progress in the development of geometrically structured nanomaterials and associated devices is summarized. First, a brief introduction of advanced nanofabrication methods that enable the fabrication of various geometrically structured nanomaterials is given, and then the performance enhancements achieved in devices utilizing these nanomaterials, namely, i) physical and gas nanosensors, ii) nanoelectromechanical devices, and iii) nanosieves are described. For the device applications, a systematic summary of their structures, working mechanisms, fabrication methods, and output performance is provided. Particular focus is given to how device performance can be enhanced through the geometric structures of the nanomaterials. Finally, perspectives on the development of novel nanomaterial structures and associated devices are presented.     

Real‐Time Imaging of Dynamic Cell Reprogramming with Nanosensors

Cellular reprogramming, the process by which somatic cells regain pluripotency, is relevant in many disease modeling, therapeutic, and drug discovery applications. Molecular evaluation of reprogramming (e.g., polymerase chain reaction, immunostaining) is typically disruptive, and only provides snapshots of phenotypic traits. Gene reporter constructs facilitate live‐cell evaluation but is labor intensive and may risk insertional mutagenesis during viral transfection. Herein, the utilization of a non‐integrative nanosensor is demonstrated to visualize key reprogramming events in situ within live cells. Principally based on sustained intracellular release of encapsulated molecular probes, nanosensors successfully monitored mesenchymal‐epithelial transition, pluripotency acquisition, and transdifferentiation events. Tracking the dynamic expression of four pivotal biomarkers (i.e., THY1, E‐CADHERIN, OCT4, and GATA4 mRNA), nanosensor signal showed great agreement with polymerase chain reaction and gene reporter imaging (R² > 0.9). Overall, such facile, versatile nanosensor enables real‐time monitoring of low‐frequency reprogramming events, thereby useful for high‐throughput assessment, optimization, and biomarker‐specific cell enrichment.     

Nanosensors for Continuous and Noninvasive Monitoring of Mesenchymal Stem Cell Osteogenic Differentiation

Assessing mesenchymal stem cell (MSC) differentiation status is crucial to verify therapeutic efficacy and optimize treatment procedures. Currently, this involves destructive methods including antibody‐based protein detection and polymerase chain reaction gene analysis, or laborious and technically challenging genetic reporters. Development of noninvasive methods for real‐time differentiation status assessment can greatly benefit MSC‐based therapies. This report introduces a nanoparticle‐based sensing platform that encapsulates two molecular beacon (MB) probes within the same biodegradable polymeric nanoparticles. One MB targets housekeeping gene glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) as an internal reference, while another detects alkaline phosphatase (ALP), a functional biomarker. Following internalization, MBs are gradually released as the nanoparticle degrades. GAPDH MBs provide a stable reference signal throughout the monitoring period (18 days) regardless of differentiation induction. Meanwhile, ALP mRNA undergoes well‐defined dynamics with peak expression observed during early stages of osteogenic differentiation. By normalizing ALP‐MB signal with GAPDH‐MB, changes in ALP expression can be monitored, to noninvasively validate osteogenic differentiation. As proof‐of‐concept, a dual‐colored nanosensor is applied to validate MSC osteogenesis on 2D culture and polycaprolactone films containing osteo‐inductive tricalcium phospate.     

Fluorescent Nanosensors Based on Colloidal Quantum Dots for the Determination of Reduced Glutathione

Measurement Techniques - A fluorescent nanosensor based on colloidal quantum dots CdSe/ZnS modified with mercaptoacetic acid to determine reduced glutathione, a non-protein compound that plays an...     

Zinc‐Dithizone Complex Engineered Upconverting Nanosensors for the Detection of Hypochlorite in Living Cells

Current chemo/biosensors for hypochlorous acid or hypochlorite detections are usually limited to the submicromolar level because of their insufficient sensitivity, which is a problem because the concentrations in biological matrices is generally on the nanomolar scale or even lower. Developing a probe with a high enough sensitivity remains a challenge. Using the minimal background fluorescence of upconversion nanocrystals to our advantage, we herein report on an energy‐transfer mechanism‐based upconversion luminescent nanosensor for the sensitive and selective detection of hypochlorite in aqueous solution. In this nanosensor water‐dispersible upconversion nanoparticles act as the energy donor and a novel hypochlorite‐responsive coordination complex Zn(DZ)₃ is employed as the energy acceptor. The quenched upconversion luminescence, induced by the Zn(DZ)₃ complex, can be efficiently recovered after addition of hypochlorite through the selective oxidative breakage of the Zn‐S‐C bonds in the Zn(DZ)₃ complex, which was verified by mass spectrometry. The detection limit for hypochlorite of this sensing system is as low as 3 nM. Furthermore, this newly coordination‐complex engineered upconversion nanosensor is successfully applied to image different amounts of exogenous hypochlorite in living HeLa cells.     

Localized Synthesis of Iron Oxide Nanowires and Fabrication of High Performance Nanosensors Based on a Single Fe2O3 Nanowire

A composed morphology of iron oxide microstructures covered with very thin nanowires (NWs) with diameter of 15–50 nm has been presented. By oxidizing metallic Fe microparticles at 255 °C for 12 and 24 h, dense iron oxide NW networks bridging prepatterned Au/Cr pads are obtained. X‐ray photoelectron spectroscopy studies reveal formation of α‐Fe₂O₃ and Fe₃O₄ on the surface and it is confirmed by detailed high‐resolution transmission electron microscopy and selected area electron diffraction (SAED) investigations that NWs are single phase α‐Fe₂O₃ and some domains of single phase Fe₃O₄. Localized synthesis of such nano‐ and microparticles directly on sensor platform/structure at 255 °C for 24 h and reoxidation at 650 °C for 0.2–2 h, yield in highly performance and reliable detection of acetone vapor with fast response and recovery times. First nanosensors on a single α‐Fe₂O₃ nanowire are fabricated and studied showing excellent performances and an increase in acetone response by decrease of their diameter was developed. The facile technological approach enables this nanomaterial as candidate for a range of applications in the field of nanoelectronics such as nanosensors and biomedicine devices, especially for breath analysis in the treatment of diabetes patients.     

Controllable Synthesis of 3D Ni(OH)2 and NiO Nanowalls on Various Substrates for High‐Performance Nanosensors

Large‐area and uniform three‐dimensional (3D) β‐Ni(OH)₂ and NiO nanowalls were synthesized on a variety of rigid and flexible substrates via a simple aqueous chemical deposition process. The β‐Ni(OH)₂ nanowalls consist of single‐crystal Ni(OH)₂ nanosheets that were vertically grown on different substrates. The height, crystallinity, and morphology of the Ni(OH)₂ nanowalls can be readily modified by adjusting the reaction time and concentration of the NiCl₂ solution. The synthesis mechanism of the Ni(OH)₂ nanowalls was determined through heterogeneous nucleation and subsequent oriented crystal growth. 3D NiO nanowalls were obtained by thermal decomposition of the Ni(OH)₂ nanowalls at 400 °C in Ar atmosphere. Highly sensitive, selective gas sensors and electrochemical sensors based on these NiO nanowalls were developed. The chemiresistive gas sensors based on the NiO nanowalls grown on ceramic substrates exhibited an excellent performance with low detection limit for formaldehyde (8 ppb) and NO₂ (15 ppb). The electrochemical sensor based on the NiO nanowalls grown on an FTO glass substrate had a superior selectivity to non‐enzymatic glucose with a detection limit of 200 nm .     

Prof. Dipl.-Ing. Dr. techn. Dr. h. c. Wilhelm Schneider

Summary In order to provide a firmer foundation on which some reciprocity theorems in Eshelbian mechanics where established earlier, a nonlinear and then linearized formulation of these theorems is presented. To carry out the required operations a simple two-degrees-of-freedom system was chosen. The analysis led to mostly algebraic expressions which are also illustrated graphically. Readers will be very sad to learn of the mournful death on January 7, 2007, of Prof. Dr. sc. techn. Dr. h. c. George Herrmann. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday