Herein, we investigate the impact of metabolic stress as a result

Herein, we investigate the impact of metabolic stress as a result of inefficient feeding utilizing a novel perfusion bioreactor and a mathematical model to achieve bioprocess improvement. Methodology/Principal Findings: To characterize nutritional requirements, the expansion of undifferentiated murine ESCs (mESCs) encapsulated in hydrogels was performed in batch and perfusion cultures using bioreactors. Despite sufficient nutrient and growth factor provision, the accumulation of inhibitory metabolites resulted in the unscheduled differentiation of mESCs and a decline in their cell numbers in the

batch cultures. Nutlin-3 price In contrast, perfusion cultures maintained metabolite concentration below toxic levels, resulting in the robust expansion ( bigger than 16-fold) of high quality ‘naive’ mESCs within 4 days. A multi-scale mathematical model describing population segregated growth kinetics, metabolism and the expression of selected pluripotency (stemness) genes was implemented to maximize information from available experimental data. A global sensitivity analysis (GSA) was employed that identified significant (6/29) model parameters and enabled model validation. Predicting

the preferential propagation of undifferentiated ESCs in perfusion culture conditions demonstrates synchrony between theory and experiment. Conclusions/Significance: The limitations of batch culture highlight the importance of cellular metabolism in maintaining pluripotency, which necessitates the design of suitable ESC bioprocesses. We propose a novel investigational framework that integrates Selleckchem LB-100 a novel perfusion culture platform (controlled metabolic conditions) with mathematical modeling (information maximization) to enhance ESC bioprocess

productivity and facilitate bioprocess optimization.”
“The purpose of the study was to describe a pedigree with NEFL E396K mutation associated with a novel dominant intermediate Charcot-Marie-Tooth disease (DI-CMT) phenotype. The pedigree comprised four patients over two generations, aged between 35 and 59 years, who have been serially evaluated since Selleckchem HDAC inhibitor 1993. Their clinical picture was characterized by pes cavus, sensorimotor neuropathy and spastic gait. Both older patients showed ascending leg weakness to involve pelvic musculature. CMT neuropathy score ranged from 14 to 26 (moderate to severe disease). Electrophysiology showed uniform nerve conduction slowing in the intermediate range, both in distal and proximal nerve segments. Multimodal evoked potential and blink reflex studies revealed abnormalities indicative of central sensorimotor pathway dysfunction. On imaging studies of lower-limb musculature, there was massive atrophy of intrinsic foot muscles and to a lesser degree of calves and thighs predominating in muscles innervated by tibial and sciatic nerves.

392) The aneurysm dome size showed a negative linear

392).\n\nThe aneurysm dome size showed a negative linear

correlation with intra-aneurysmal flow velocity and WSS. find more Wide-necked aneurysm geometry was associated with faster intra-aneurysmal flow velocity.”
“Penile precancerous and invasive lesions exhibit a variegated morphology. Although the diagnosis and classification of penile tumors is straightforward in most cases, a few entities are problematic, especially to pathologists from countries in which penile cancer is rarely encountered. The differential diagnosis of squamous hyperplasias from differentiated penile intraepithelial neoplasia or from extremely low-grade invasive neoplasms (eg, pseudohyperplastic and verrucous carcinomas) may be particularly check details difficult. Similarly, given the morphologic features shared by all verruciform tumors (ie, verrucous, warty, papillary, and cuniculatum carcinomas, along with giant condylomas), it is challenging at times to distinguish one from another. At the other end of the spectrum, because of their lack of differentiation, it is sometimes difficult to classify high-grade carcinomas, such as basaloid and sarcomatoid,

which may have etiologic/prognostic implications. Penile mixed tumors, harboring more than 1 histologic subtype and grade, constitute a frequent finding in routine pathology. The recognition of distinctive morphologic patterns and histologic grades in these tumors is important because these features could be related to etiologic factors, such as human papillomavirus infection, or they could influence outcome. Penile tumors with glandular features (eg,

adenosquamous and mucoepidermoid carcinomas), although rare, may be confused with HM781-36B nmr the more common pseudoglandular (adenoid, acantholytic) variant of squamous cell carcinomas, their main mimicker. In this review we provide clues that may help in the differential diagnosis of these lesions. (C) 2012 Elsevier Inc. All rights reserved.”
“Diagnostic accuracy can be improved considerably by combining multiple biomarkers. Although the likelihood ratio provides optimal solution to combination of biomarkers, the method is sensitive to distributional assumptions which are often difficult to justify. Alternatively simple linear combinations can be considered whose empirical solution may encounter intensive computation when the number of biomarkers is relatively large. Moreover, the optimal linear combinations derived under multivariate normality may suffer substantial loss of efficiency if the distributions are apart from normality. In this paper, we propose a new approach that linearly combines the minimum and maximum values of the biomarkers. Such combination only involves searching for a single combination coefficient that maximizes the area under the receiver operating characteristic (ROC) curves and is thus computation-effective.

Kinematics and kinetics were recorded using an instrumented trans

Kinematics and kinetics were recorded using an instrumented transfer assessment system. Based on kinetic and kinematic measurements, a relative threshold-based algorithm was developed to identify

four distinct phases: pre-lift, upper arm loading, lift-pivot and post-lift phases. To determine the stability of the algorithm between the two SPTs, Student t-tests for dependent samples were performed on the absolute duration of each phase.\n\nResults: The mean total duration of the SPT was 2.00 +/- 0.49 s. The mean duration of the pre-lift, upper arm loading, lift-pivot and post-lift phases were 0.74 +/- 0.29 s, 0.28 +/- 0.13 s, 0.72 +/- 0.24 s, 0.27 +/- 0.14 s whereas their relative contributions represented approximately 35%, 15%, 35% and 15% of the overall SPT cycle, respectively. No significant differences were found between the trials (p = 0.480-0.891).\n\nConclusion: The relative threshold-based algorithm this website used to automatically detect the four distinct phases of the SPT, is rapid, accurate and repeatable. A quantitative and thorough description

of the precise phases of the SPT is prerequisite to better interpret biomechanical findings and measure task performance. The algorithm could also become clinically useful to refine the assessment and training of SPTs.”
“Aim To assess the QNZ order accuracy and reproducibility of biometry undertaken with the Aladdin (Topcon, Tokyo, VX809 Japan) in comparison with the current gold standard device, the IOLMaster 500 (Zeiss, Jena, Germany). Setting University Eye Clinic, Birmingham, UK and Refractive Surgery Centre, Kiel, Germany. Methods The right eye of 75 patients with cataracts and 22 healthy participants were assessed using the two devices. Measurements of axial length (AL), anterior chamber depth (ACD) and keratometry (K) were undertaken with the Aladdin and IOLMaster 500 in random order by an experienced practitioner. A second practitioner then obtained measurements

for each participant using the Aladdin biometer in order to assess interobserver variability. Results No statistically significant differences (p bigger than 0.05) between the two biometers were found for average difference (AL)+/- 95% CI=0.01 +/- 0.06 mm), ACD (0.00 +/- 0.11 mm) or mean K values (0.08 +/- 0.51 D). Furthermore, interobserver variability was very good for each parameter (weighted kappa bigger than = 0.85). One patient’s IOL powers could not be calculated with either biometer measurements, whereas a further three could not be analysed by the IOLMaster 500. The IOL power calculated from the valid measurements was not statistically significantly different between the biometers (p=0.842), with 91% of predictions within +/- 0.25 D. Conclusions The Aladdin is a quick, easy-to-use biometer that produces valid and reproducible results that are comparable with those obtained with the IOLMaster 500.

Conclusion Inducible

ischaemia is highly prevalent in

\n\nConclusion Inducible

ischaemia is highly prevalent in male siblings, suggesting a previously unknown long quiescent period before the occurrence of a clinical event. While inducible ischaemia is associated with a worse prognosis, male siblings with negative tests still bear a high risk of incident disease, such that we propose that in male siblings over 40 years of age, aggressive primary prevention GSI-IX interventions be instituted without nuclear testing. For women, the prevalence of ischaemia was so low as to not warrant screening, but the incidence of CAD was high enough to at least warrant lifestyle interventions.”
“Purpose The purpose of this qualitative descriptive study find more was to explore the sociocultural influences and social context associated with living with type 2 diabetes among migrant Latino adults.\n\nMethods A qualitative descriptive study using grounded theory techniques was conducted. In-depth semistructured interviews were completed with 10 participants (6 female and 4 male) ranging in age from 46 to 65 years and with a duration of diabetes diagnosis ranging from 1.5 to 40 years.\n\nResults An overarching meta-theme of self-management in a social environment emerged. Every aspect of the process of self-management, as described in the 4 major themes-(1) family cohesion, (2) social stigma

of disease, (3) social expectations/perception of “illness,” and (4) disease knowledge and understanding-was influenced by the social context.\n\nConclusions The familist traditions, central to the Mexican culture, had both positive and negative consequences on diabetes management. Tailoring clinical care and developing novel education approaches, to include family and community, is central to improving the health of this population. Recognizing and acknowledging the social stigma associated with diabetes, for this population, will promote understanding and improve clinician-patient communication. The sociocultural influences that affect diabetes management practices (eg, include family, in particular the primary LY3023414 female

caregiver, and establish community- and home-based education sessions) must be integrated into clinical practice. Future research focused on population-defined health and disease self-management, novel educational interventions, and family and community interventions focusing on the concept of social stigma of disease is indicated to further affect the health disparities of this population.”
“Ivermectin is a commonly used veterinary drug that may cause serious problems in overdose situations. A retrospective study was completed, which evaluated canine exposures to ivermectin from 1998 to 2005. The cases were evaluated based on ivermectin dosage, clinical signs seen, signalment of the animal involved, and the potential that the animal could have a pc glycoprotein defect.

The chemical structures of precursory networks and resulting poro

The chemical structures of precursory networks and resulting porous thermosetting films were confirmed by FTIR analysis and gel fraction determination. The porosity of the latter films was examined by SEM and DSC-based thermoporometry. Average pore diameters were found to be lower than 50 nm and pore volumes as high as 0.16 cm(3) g(-1) selleck chemical were determined. The density values of porous samples were found to be lower than that of non-porous pure PCN synthesized as a model system, thus suggesting the occurrence of closed pore structures. Moreover, the thermal properties of PCN-based films were investigated by DSC and TGA. The high-boiling temperature liquids decreased their glass transition temperatures

(T-g) and their degradation temperatures by acting as plasticizers. This plasticizing effect logically disappeared after removal of pore-forming phthalates from the networks: the T-g values of the mesoporous films were even higher than that of non-porous neat PCN, while their thermal stability turned out to be nearly identical to that of neat PCN. (C) 2013 Elsevier

Ltd. All rights reserved.”
“Performing 2 highly similar tasks at the same time requires an adaptive regulation of cognitive control to shield prioritized primary task processing from between-task (cross-talk) interference caused by secondary task processing. In the present study, p38 MAPK inhibitors clinical trials the authors investigated how implicitly and explicitly delivered information promotes the flexible online adjustment of task shielding in dual-task performance. Context-specific implicit activation of cognitive control was implemented by location-dependent Citarinostat manipulations of the likelihood of between-task interference (i.e., locations containing high vs. low proportions of between-task interference trials). Following practice, between-task interference was reduced in a subsequent test session for locations associated with high (compared to locations with low) task-shielding demands, indicating that the cognitive system can register and utilize implicit context features (Experiments 1 and 2). In Experiment 3, cues were used that provided additional explicit information.

Whereas cues validly indicating the interference level in the next trial failed to further optimize context-specific task shielding, cues indicating the location of subsequent stimulus presentation resulted in an instant adjustment of task shielding already in the first part of the experiment. Results highlight the role of implicit and explicit information for context-sensitive adjustments of cognitive control in dual-task performance.”
“Due to the strong dependence of tissue electrical properties on temperature, it is important to consider the potential effects of intense tissue heating on the RF electromagnetic fields during MRI, as can occur in MR-guided focused ultrasound surgery. In principle, changes of the RF electromagnetic fields could affect both efficacy of RF pulses, and the MRI-induced RF heating (SAR) pattern.

The C-3 cycle enzyme sedoheptulose-1,7 bisphosphatase (SBPase, EC

The C-3 cycle enzyme sedoheptulose-1,7 bisphosphatase (SBPase, EC has been shown to exert strong metabolic control over RuBP regeneration at light saturation.\n\nResults: We tested the hypothesis that tobacco transformed to overexpressing SBPase Vorinostat inhibitor will exhibit greater stimulation of A than wild type (WT) tobacco when grown under field conditions at elevated [CO2] (585 ppm) under fully open air fumigation. Growth under elevated [CO2] stimulated instantaneous A and the diurnal photosynthetic integral (A’) more in transformants than WT. There was evidence of photosynthetic acclimation to elevated [CO2] via downregulation of V-c,V-max in both

WT and transformants. Nevertheless, greater carbon assimilation and electron transport rates (J and J(max)) for transformants led to greater yield increases than WT at elevated this website [CO2] compared to ambient grown plants.\n\nConclusion: These results provide proof of concept that increasing content and activity of a single photosynthesis enzyme can enhance carbon assimilation and yield of C-3 crops grown at [CO2] expected by the middle of the 21st century.”
“The effects of Si doping on the evolution of stress in AlxGa1-xN:Si thin films (x approximate to 0.4-0.6) grown on 6H-SiC by metal organic chemical vapor deposition were investigated using

in situ wafer curvature measurements. The results were correlated with changes in film microstructure as observed by transmission electron microscopy. The incorporation of Si into the films resulted in a compressive-to-tensile transition in the biaxial stress at the surface, and the magnitude of the tensile stress

was found to increase in proportion to the Si concentration. The stress gradient was attributed to Si-induced dislocation inclination resulting from an effective climb mechanism. Si doping also resulted in a decrease in the threading dislocation density in the AlxGa1-xN layers, which was attributed to increased dislocation GSK2245840 interaction and annihilation. The model describing tensile stress generated by dislocation effective climb was modified to account for the dislocation reduction and was found to yield an improved fit to the experimental stress-thickness data. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3160331]“
“Significant differences exist in the respiratory adaptation to exercise in different equine breeds. This research describes the ergoespirometric response to exercise of Andalusian (AN) and Arabian (A) horses, both selected according to morphological criteria. Thirteen untrained male horses (6 AN and 7 A) performed a treadmill exercise test (TET) with a slope of 6%, with workloads starting from 5 m/s and increasing 1 m/s every 3 min until the horses were not able to keep the required velocity.

ROS-elevating and ROS-depleting anticancer strategies and their m

ROS-elevating and ROS-depleting anticancer strategies and their mechanisms are thoroughly discussed. We argue that the rationale for therapy choice depends on a complete understanding of cancer cell redox state, namely, the “redox signaling signature” of cancer.”
“We have recently reported the discovery of pyrrolo[3,2-d] pyrimidine derivatives 1a and 1b as potent triple inhibitors of vascular endothelial growth factor receptor

(VEGFR), platelet-derived growth factor receptor (PDGFR), and Tie-2 kinases. To identify compounds having strong inhibitory activity VX809 against fibroblast growth factor receptor (FGFR) kinase, further modification was conducted using the co-crystal structure analysis of VEGFR2 and 1b. Among the compounds synthesized, urea derivative 11l having a piperazine moiety on the terminal benzene ring showed strong inhibitory activity against FGFR1 kinase as well as VEGFR2 kinase. A binding model of 11l

complexed with VEGFR2 suggested that the piperazine moiety forms additional interactions with Ile1025 and His1026. (C) 2010 Elsevier Ltd. All rights reserved.”
“Concentrations of cadmium, mercury and lead were analysed by atomic absorption spectrometry in the kidney and muscle of free-living wild boar (n = 169) from hunting grounds in seven counties of continental Croatia. Mean levels of metals (mg/kg) in muscle and kidney of boars ranged as follows: Cd: 0.005-0.016 Cell Cycle inhibitor and 0.866-4.58, Pb: 0.033-0.15 and 0.036-0.441, Hg: 0.004-0.012 and 0.04-0.152. In all seven regions, concentrations exceeded the permitted values (muscle and kidney mg/kg: cadmium 0.05/1; lead 0.1/0.5; mercury 0.03/0.1) in 13.6% and 71.6% of samples (muscle and kidney, respectively) for cadmium; 13.6% and 8.9% for lead; 19.5% and 2.4% for mercury. There were significant differences among the regions. Vukovar-Srijem and Virovitica-Podravina VX-809 Transmembrane Transporters inhibitor Counties were highly contaminated with cadmium, Sisak-Moslavina and Virovitica-Podravina Counties with lead and Brod-Posavina County had highest mercury concentrations. These

results suggest a detailed investigation of physiological and environmental factors contributing to accumulation of metals in boars.”
“The discovery of a second estrogen receptor, ER beta, and the finding that 5 alpha-androstane-3 beta,17 beta-diol (3 beta Adiol) strongly binds to ER beta, have opened up a new aspect of estrogen signaling. Some of the major shifts in our understanding come from finding ER beta in tissues which do not express ER alpha but are estrogen-responsive; these were called sites of ‘indirect estrogen action’. Two key sites that fall into this category are the brain and the prostate. Studies of ER beta in the past 10 years have led us to hypothesize that estrogen signaling depends on the balance between ER alpha and ER beta, and that inadequate predominance of one or the other isoform could lead to disease.

In the same group of subjects, imaging and measurements were repe

In the same group of subjects, imaging and measurements were repeated using BK Medical Flex Focus 400 ultrasound system

with linear (18 MHz) and curved 5 (MHz) transducers. The MobiUS system was also used to image plastic cylinders and procedure needles embedded in tofu bars. Outside diameters of cylinders were measured using digital calipers and sonography.\n\nResults: The mean diameter of the hyomental muscle in 10 healthy volunteers was 7.22 +/- 1.6 mm using BK 18 MHzprobe, 7.11 +/- 1.7mmusing MobiUS 7.5 MHz probe, and 7.84 +/- 2 mm using MobiUS 3.5 MHz probe. These means were not statistically different (BK vs Mo 7.5, P = .74, and BK vs Mo 3.5, P = .13). The mean outside diameter of plastic cylinders Smoothened Agonist measured with digital calipers was 10.1 +/- 0.2 mm (n = 5) vs 9.8 +/- 0.3 mm and 10.2 +/- 0.2 mm using 3.5 and 7.5 MHz probes, respectively. These means were not statistically different (calipers vs Mo

3.5, P = .16 and calipers vs Mo 7.5, P = .39).\n\nConclusion: Mobisante MobiUS system was able to acquire clinically useful images of the suprahyoid airway and muscular architecture in the mouth floor and allowed accurate measurements ACY-738 datasheet of linear distances. (C) 2013 Elsevier Inc. All rights reserved.”
“An effective method for mass production of field-emission microcathodes (mu FECs) is suggested and described. The main properties of the mu FECs are calculated using the actual geometric parameters of the system (emitting nanotip radius similar to 15-20 nm, interelectrode distance similar to 1.5-2 mu m, etc.). It is shown that the electric field strength in the immediate vicinity of a nanotip is several units of 10(7) V/cm at comparatively low (100-200 V) voltages applied. A series of probable applications taking advantage of the unique features of the mu FECs Bcl-2 inhibitor are suggested. (C) 2010 Elsevier B.V. All rights reserved.”
“To address the pressing need for better in vitro testicular toxicity models, a workshop sponsored by the International Life Sciences Institute (ILSI), the Health and Environmental

Science Institute (HESI), and the Johns Hopkins Center for Alternatives to Animal Testing (CAAT), was held at the Mt. Washington Conference Center in Baltimore, MD, USA on October 26-27, 2011. At this workshop, experts in testis physiology, toxicology, and tissue engineering discussed approaches for creating improved in vitro environments that would be more conducive to maintaining spermatogenesis and steroidogenesis and could provide more predictive models for testicular toxicity testing. This workshop report is intended to provide scientists with a broad overview of relevant testicular toxicity literature and to suggest opportunities where bioengineering principles and techniques could be used to build improved in vitro testicular models for safety evaluation. Tissue engineering techniques could, conceivably, be immediately implemented to improve existing models.

PKG did not affect protein stability, nor did it increase phospho

PKG did not affect protein stability, nor did it increase phosphorylation of the amino-terminal Ser33/37/Thr41 residues that are known to target beta-catenin

for degradation. However, we found that PKG potently inhibited transcription from a luciferase reporter driven by the human CTNNB1 promoter, and this corresponded to reduced beta-catenin C59 solubility dmso mRNA levels. Although PKG was able to inhibit transcription from both the CTNNB1 and TCF reporters, the effect on protein levels was less consistent. Ectopic PKG had a marginal effect on beta-catenin protein levels in SW480 and HCT116 but was able to inhibit TCF-reporter activity by over 80%. Investigation of alternative mechanisms revealed that cJun-N-terminal kinase (JNK) activation

was required for the PKG-dependent regulation of TCF activity. PKG activation caused beta-catenin to bind to FOXO4 in colon cancer cells, PKC412 price and this required JNK. Activation of PKG was also found to increase the nuclear content of FOXO4 and increase the expression of the FOXO target genes MnSOD and catalase. FOXO4 activation was required for the inhibition of TCF activity as FOXO4-specific short-interfering RNA completely blocked the inhibitory effect of PKG. These data illustrate a dual-inhibitory effect of PKG on TCF activity in colon cancer cells that involves reduced expression of beta-catenin at the transcriptional level, and also beta-catenin sequestration by FOXO4 activation. Oncogene (2010) 29, 3423-3434; doi:10.1038/onc.2010.91; published online 29 March 2010″
“Evidence supports that oxidative stress exerts significant effects on the pathogenesis of heart dysfunction. On the other hand, the presence of specific androgen receptor (AR) in mammalian cardiomyocytes implies that androgen plays a physiological role in cardiac function, myocardial injury and the regulation of the redox state in the heart. This study used the testicular feminized (Tfm) and castrated

male mice to investigate the effects of testosterone deficiency, physiological testosterone therapy and AR on oxidative stress in cardiomyocytes. Tfm mice have a non-functional selleckchem AR and reduced circulating testosterone levels. Male littermates and Tfm mice were separated into 5 experimental groups: non-castrated littermate controls, castrated littermates, sham-operated Tfm, testosterone-treated castrated littermates and testosterone-treated sham-operated Tfm mice. Cardiomyocytes that were isolated from the left ventricle were used far determination of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) enzyme activities, and malondialdehyde (MDA) levels. Additionally, mitochondrial DNA (rntDNA) deletion mutations were detected by nested PCR. The SOD and GSH-Px enzyme activities of cardiomyocytes were decreased, and the MDA levels and the proportion of mtDNA, mutations were increased in castrated and sham-operated Tfm mice compared to control mice.

Network-based intervention involving older

Network-based intervention involving older SB273005 cost individuals to provide encouragement to younger network members should be explored as a means to increase motivation to screen among this population. (Am J Prev Med 2010,38(4) 396-402) Published by Elsevier Inc on behalf of American Journal of Preventive Medicine”
“A total of 695 fat-tailed Barbarine lambs born in two flocks between 1995 and 1997 were recorded for growth and fat tail measurements according to “standard growth recording protocol”. Recorded traits are body weight (BW) and the following fat tail characteristics: upper circumference (UFTC), lower circumference (LFTC),

upper width (UFTW), lower width (LFTW), upper depth (UFTD), lower depth (LFTD) and tail length (FTL). Lamb body growth performance and tail measurements are analyzed from

two points of view. Firstly through the adjustment of a growth curve chosen among the following: Brody, Logistic, Gompertz and Bertalanffy functions. Secondly, age-adjusted weight and tail measurements (10, 30 and 70 days) were analyzed and average daily gains (ADG) were calculated.\n\nAll functions (Brody, Logistic, Gompertz and Bertalanffy) fitted closely body weight and fat tail measurements of Barbarine lambs for the recording period (up to 120 days), while the Bertalanffy function provided more accurate Fludarabine inhibitor Vorinostat estimation of

the asymptotic value (adult size) for the weight and tail measurements. High significant correlations (p<0.01) were obtained between body weight and tail measurements. However, the LFTW-ADG had the highest correlation with BW performance, and was therefore the best indicator of the state of lamb fattening. Furthermore, the LFTW-ADG recorded between 10 and 30 days of age has a higher correlation with lamb BW performance at later age (30-70 days) than those recorded at the same period (between 10 and 30 days), indicating that lambs with higher fat storage during the suckling period express better performance at later ages. Therefore, this study confirms the role of the tail fat as an adaptive character of the Barbarine breed and most likely of other fat-tailed sheep breeds. (C) 2010 Elsevier B.V. All rights reserved.”
“Nanoporous anodic alumina (NAA) is a material with great interest in nanotechnology and with promising applications to biotechnology. Obtaining specific and regularly functionalized NAA surfaces is essential to obtain meaningful results and applications. Silane-PEG-NHS (triethoxysilane-polyethylene-glycol-N-hydroxysuccinimide) is a covalent linker commonly used for single-molecule studies.