The Next Generation: Surgeon Learning Curve in a Mature Operative Rib Management Program.

INTRODUCTION: Prior work has demonstrated utility in using operative time to measure surgeon learning for surgical stabilization of rib fractures (SSRF); however, no studies have used operative time to evaluate the benefit of proctoring in subsequent generations of surgeons. We sought to evaluate whether there is a difference in learning between an original series (TOS) of self-taught surgeons versus the next generation (TNG) of proctored surgeons using cumulative summation (CUSUM) analysis. We hypothesized that TNG would have a comparatively accelerated learning curve. METHODS: A single-center retrospective review of all SSRF at a level 1 trauma center was performed. Data were collected from the beginning of an operative chest injury program to include at least 2 y of TNG experience. Operative time was used to determine success and misstep based on prior methods. Learning curves using CUSUM analysis were calculated based on an anticipated success rate of 90% and compared between TOS and TNG groups. RESULTS: Over 7 y, 163 patients with a median Injury Severity Score of 24 underwent SSRF. Median operative time was 165 min with a 0.5 plate-to-fracture ratio. All three TOS surgeons experienced a positive slope indicative of early missteps for their first 15-20 cases. By contrast, all three TNG surgeons demonstrated a series of early successes resulting in negative CUSUM slopes which coincided with a period of proctoring. By the end of TNG series, the composite cumulative score was less than half of the TOS surgeon' scores. CONCLUSIONS: Operative time continues to be a useful surrogate for observing SSRF learning curves. In a mature institutional program, proctored novice surgeons appear to have an accelerated learning curve compared to novice surgeons developing a new operative rib program.

Trends in heart failure costs for commercially insured patients in the United States (2006-2021).

BACKGROUND: Although prior research has estimated the overarching cost burden of heart failure (HF), a thorough analysis examining medical expense differences and trends, specifically among commercially insured patients with heart failure, is still lacking. Thus, the study aims to examine historical trends and differences in medical costs for commercially insured heart failure patients in the United States from 2006 to 2021. METHODS: A population-based, cross-sectional analysis of medical and pharmacy claims data (IQVIA PharMetrics® Plus for Academic) from 2006 to 2021 was conducted. The cohort included adult patients (age > = 18) who were enrolled in commercial insurance plans and had healthcare encounters with a primary diagnosis of HF. The primary outcome measures were the average total annual payment per patient and per cost categories encompassing hospitalization, surgery, emergency department (ED) visits, outpatient care, post-discharge care, and medications. The sub-group measures included systolic, diastolic, and systolic combined with diastolic, age, gender, comorbidity, regions, states, insurance payment, and self-payment. RESULTS: The study included 422,289 commercially insured heart failure (HF) patients in the U.S. evaluated from 2006 to 2021. The average total annual cost per patient decreased overall from $9,636.99 to $8,201.89, with an average annual percentage change (AAPC) of -1.11% (95% CI: -2% to -0.26%). Hospitalization and medication costs decreased with an AAPC of -1.99% (95% CI: -3.25% to -0.8%) and - 3.1% (95% CI: -6.86-0.69%). On the other hand, post-discharge, outpatient, ED visit, and surgery costs increased by an AAPC of 0.84% (95% CI: 0.12-1.49%), 4.31% (95% CI: 1.03-7.63%), 7.21% (95% CI: 6.44-8.12%), and 9.36% (95% CI: 8.61-10.19%). CONCLUSIONS: The study's findings reveal a rising trend in average total annual payments per patient from 2006 to 2015, followed by a subsequent decrease from 2016 to 2021. This decrease was attributed to the decline in average patient costs within the Medicare Cost insurance category after 2016, coinciding with the implementation of the Medicare Access and CHIP Reauthorization Act (MACRA) of 2015. Additionally, expenses related to surgical procedures, emergency department (ED) visits, and outpatient care have shown substantial growth over time. Moreover, significant differences across various variables have been identified.

Approaching toxigenic Clostridia from a One Health perspective.

Spore-forming pathogens have a unique capacity to thrive in diverse environments, and with temporal persistence afforded through their ability to sporulate. Their prevalence in diverse ecosystems requires a One Health approach to identify critical reservoirs and outbreak-associated transmission chains, given their capacity to freely move across soils, waterways, foodstuffs and as commensals or infecting pathogens in human and animal populations. Among anaerobic spore-formers, genomic resources for pathogens including C. botulinum, C. difficile, and C. perfringens enable our capacity to identify common and unique factors that support their persistence in diverse reservoirs and capacity to cause disease. Publicly available genomic resources for spore-forming pathogens at NCBI's Pathogen Detection program aid outbreak investigations and longitudinal monitoring in national and international programs in public health and food safety, as well as for local healthcare systems. These tools also enable research to derive new knowledge regarding disease pathogenesis, and to inform strategies in disease prevention and treatment. As global community resources, the continued sharing of strain genomic data and phenotypes further enhances international resources and means to develop impactful applications. We present examples showing use of these resources in surveillance, including capacity to assess linkages among clinical, environmental, and foodborne reservoirs and to further research investigations into factors promoting their persistence and virulence in different settings.

Electrochemical Analysis of the Thermal Stability of 0.9-4.1 nm Diameter Gold Nanoclusters.

Here we report the thermal properties of weakly stabilized 0.9, 1.6, and 4.1 nm Au nanoparticles (NPs)/nanoclusters (NCs) attached to indium-tin-oxide- or fluorine-doped-tin-oxide-coated glass electrodes (glass/ITO or glass/FTO). The peak oxidation potential (Ep) for Au measured by anodic stripping voltammetry (ASV) is indicative of the NP/NC size. Heating leads to a positive shift in Ep due to an increase in NP/NC size from thermal ripening. The size transition temperature (Tt) decreases with decreasing NP/NC size following the order of 4.1 nm (509 °C) > 1.6 nm (132 °C) > 0.9 nm (90 °C/109 °C, two transitions) as compared to the bulk melting point (Tm,b) for Au of 1064 °C. The Tt generally agrees with models describing the size-dependent melting point of Au NPs (Tm,NP) for 4.1 and 1.6 nm diameter Au NPs but is higher than the models for 0.9 nm Au NCs. Scanning electron microscopy (SEM) and UV-vis size analysis confirm the electrochemical results. The thermal stability of electrode-supported metal NPs/NCs is important for their effective use in catalysis, sensing, nanoelectronics, photovoltaics, and other applications.

Prospective Genomic Surveillance Reveals Cryptic MRSA Outbreaks with Local to International Origins among NICU Patients.

Methicillin-resistant Staphylococcus aureus (MRSA) infections cause substantive morbidity and mortality in neonates. Using publicly available resources from the National Center of Biotechnology Information (NCBI) and Food and Drug Administration's (FDA) GalaxyTrakr pipeline, we illustrate the dynamics of MRSA colonization and infection in neonates. Over 217 days of prospective surveillance, analyses revealed concurrent MRSA transmission chains affecting 11 of 17 MRSA-colonized patients (65%), with two clusters that demonstrated intervals of more than a month among the appearance of isolates. All MRSA infected neonates (n = 3) showed previous colonization with the infecting strain. GalaxyTrakr clustering of the NICU strains, in the context of 21,521 international isolates deposited in NCBI's Pathogen Detection Resource, revealed NICU isolates to be distinct from adult MRSA strains seen locally and internationally. Clustering of the NICU strains within an international context enhanced the resolution of strain clusters and supported the rule-out of suspected, local transmission events within the NICU. Analyses also identified sequence type 1535 isolates, emergent in the Middle East, carrying a unique SCCmec with fusC and aac(6')-Ie/aph(2'')-1a that provided a multidrug-resistant phenotype. NICU genomic pathogen surveillance, leveraging public repositories and outbreak detection tools, supports rapid identification of cryptic MRSA clusters, and can inform infection prevention interventions for this vulnerable patient population. Results demonstrate that sporadic infections in the NICU may be indicative of hidden chains of asymptomatic transmission best identified with sequenced-based approaches.

T-cell activation profiles distinguish hemophagocytic lymphohistiocytosis and early sepsis.

Hemophagocytic lymphohistiocytosis (HLH) is a fatal disorder of immune hyperactivation that has been described as a cytokine storm. Sepsis due to known or suspected infection has also been viewed as a cytokine storm. Although clinical similarities between these syndromes suggest similar immunopathology and may create diagnostic uncertainty, distinguishing them is critical as treatments are widely divergent. We examined T-cell profiles from children with either HLH or sepsis and found that HLH is characterized by acute T-cell activation, in clear contrast to sepsis. Activated T cells in patients with HLH were characterized as CD38high/HLA-DR+ effector cells, with activation of CD8+ T cells being most pronounced. Activated T cells were type 1 polarized, proliferative, and displayed evidence of recent and persistent activation. Circulating activated T cells appeared to be broadly characteristic of HLH, as they were seen in children with and without genetic lesions or identifiable infections and resolved with conventional treatment of HLH. Furthermore, we observed even greater activation and type 1 polarization in tissue-infiltrating T cells, described here for the first time in a series of patients with HLH. Finally, we observed that a threshold of >7% CD38high/HLA-DR+ cells among CD8+ T cells had strong positive and negative predictive value for distinguishing HLH from early sepsis or healthy controls. We conclude that the cytokine storm of HLH is marked by distinctive T-cell activation whereas early sepsis is not, and that these 2 syndromes can be readily distinguished by T-cell phenotypes.

Evaluating the Utility of High Sensitivity Troponin in Blunt Cardiac Injury.

INTRODUCTION: Screening for blunt cardiac injury (BCI) includes obtaining a serum troponin level and an electrocardiogram for patients diagnosed with a sternal fracture. Our institution has transitioned to the use of a high sensitivity troponin I (hsTnI). The aim of this study was to determine whether hsTnI is comparable to troponin I (TnI) in identifying clinically significant BCI. MATERIALS AND METHODS: Trauma patients presenting to a level I trauma center over a 24-mo period with the diagnosis of sternal fracture were screened for BCI. Any initial TnI more than 0.04 ng/mL or hsTnI more than 18 ng/L was considered positive for potential BCI. Clinically significant BCI was defined as a new-bundle branch block, ST wave change, echocardiogram change, or need for cardiac catheterization. RESULTS: Two hundred sixty five patients with a sternal fracture were identified, 161 underwent screening with TnI and 104 with hsTnI. For TnI, the sensitivity and specificity for detection of clinically significant BCI was 0.80 and 0.79, respectively. For hsTnI, the sensitivity and specificity for detection of clinically significant BCI was 0.71 and 0.69, respectively. A multivariate analysis demonstrated the odds ratio for significant BCI with a positive TnI was 14.4 (95% confidence interval, 3.9-55.8, P < 0.0001) versus an odds ratio of 5.48 (95% confidence interval 1.9-15.7, P = 0.002) in the hsTnI group. CONCLUSIONS: The sensitivity of hsTnI is comparable to TnI for detection of significant BCI. Additional investigation is needed to determine the necessity and interval for repeat testing and the need for additional diagnostic testing.

The heart transplant allocation change attenuates but does not eliminate blood group O waitlist outcome disadvantage.

BACKGROUND: Patients with blood group O have historically been disadvantaged in the United Network for Organ Sharing (UNOS) heart transplant allocation system. We sought to determine whether the new UNOS allocation system implemented in 2018 had an impact on waitlist and post-transplant outcomes among blood groups. METHODS: Using the UNOS database we included all adult patients listed and transplanted with first-time single-organ heart transplant between 10/17/15 and 10/1/21. For post-transplant outcomes, we separately evaluated all adult patients transplanted with the same time-frame. We used exclusion criteria and censoring to limit biases from changing clinical practices around the allocation change (10/18/2018), and from unequal or inadequate follow-up. We compared clinical characteristics and outcomes before and after the allocation change among each blood group. Fine-Gray and Cox regression models were used to estimate the effect of the new allocation system on competing waitlist outcomes- transplantation, death-or-removal from waitlist- and post-transplant survival, respectively. RESULTS: Of the 21,565 patients listed for transplantation 14,000 met criteria for waitlist analysis (7,035 in the old system vs. 6,965 in the new), and 7,657 met criteria for post-transplant analysis (3,519 in the old system vs. 4,138 in the new). Among each blood group, new allocation change was associated with higher transplantation rates lower waitlist days and lower waitlist mortality (except Group AB). However, despite improvements, Group O was still associated with worse waitlist outcomes for each metric compared to non-O Groups. The new allocation system did not have a significant impact on post-transplant survival among any blood groups. CONCLUSION: Changes in heart transplant allocation have attenuated but not eliminated blood group O disadvantage in access to donor hearts.

Impact of the heart transplant allocation policy change on inpatient cost of index hospitalization.

BACKGROUND: We sought to determine the financial impact of the United Network for Organ Sharing heart transplant (HT) allocation policy change of October 2018. METHODS: Using the Nationwide Inpatient Sample we retrospectively analyzed hospital discharge data between January 1, 2016 and December 31, 2019. ICD-10-CM procedure codes were used to identify hospitalizations of patients undergoing HT as well as the use of temporary mechanical circulatory support (MCS) during the HT hospitalization. Patients < 18 years old and those with missing data on costs were excluded. The primary outcome was inflation-adjusted costs. Total costs were inflated to 2019 US dollars. RESULTS: During the course of the study, temporary MCS increased significantly among 11 380 weighted patients transplanted while mean length of stay (LOS) did not. Mean inflation-adjusted costs rose about $40k per HT. On univariate analysis, transplantation year, use of temporary MCS and LOS were all significantly associated with increased cost while on multivariate analysis only temporary MCS and LOS were. CONCLUSIONS: The 2018 allocation change has resulted in more expensive inpatient costs for HT correlating with an increase in temporary MCS.

Low-dose colchicine reduced risk for cardiovascular events in chronic coronary disease.

SOURCE CITATION: Nidorf SM, Fiolet ATL, Mosterd A, et al. Colchicine in patients with chronic coronary disease. N Engl J Med. 2020;383:1838-47. 32865380.

The effect of recipient BMI on waitlist and post-transplant outcomes after the 2018 heart transplant allocation policy change.

OBJECTIVE: The effects of recipient body mass index (BMI) on waitlist strategies, waitlist outcomes, and post-transplant outcomes among adult patients listed for heart transplantation under the updated 2018 allocation system have not been well characterized. METHODS: The United Network of Organ Sharing data set between October 2015 and March 2021 was analyzed, and patients were grouped based on recipient BMI and whether listing occurred in the old (pre-October 2018) or new allocation system. RESULTS: Listing strategies differed by BMI group, but trends of increased use of temporary mechanical support and decreased use of durable support remained among all BMI groups, except those with BMI > 35 kg/m2 . Waitlist outcomes improved among all BMI cohorts in the new allocation system, including among patients with BMI 30-34.9 and >35 kg/m2 , although patients with higher BMIs continued to have longer waitlist times. Post-transplant outcomes in the new allocation system are worse for patients with BMI > 30 kg/m2  (hazard ratio: 1.47; confidence interval: 1.19-1.82; p < .001). CONCLUSIONS: The 2018 change to the heart transplant allocation system was associated with similar changes in the use of mechanical support for listing strategy across BMI ranges, except in the most obese, and improved waitlist outcomes across all BMI ranges. Post-transplant outcomes in the new allocation system are worse for patients with BMI > 30 kg/m2  compared to patients with BMI < 30 kg/m2 . These findings have important clinical implications for our understanding of the ongoing influence of BMI on waitlist courses and post-transplant outcomes among patients listed for heart transplantation.

Impact of heart transplant allocation change on competing waitlist outcomes among listing strategies.

In 2018, the United Network for Organ Sharing (UNOS) adopted a 6-tier system for heart allocation which shifted patterns in listing strategies. The effects of the change on waitlist survival and transplantation rates have yet to be substantiated by analysis of competing outcomes among various listing strategies. This study included all adult patients listed for first-time heart transplantation in UNOS between 10/17/15 and 6/12/20. Clinical characteristics were compared before and after allocation change among various listing strategies: no support, inotropes, intra-aortic balloon pump, durable left ventricular assist device (LVAD), temporary VAD, and extracorporeal membrane oxygenation. Fine-Gray proportional subhazard models were used to estimate the effect of allocation change on competing waitlist outcomes-transplantation, death, or removal from waitlist-among each strategy. During the study period, there were 17 422 patients listed for heart transplantation. Among each listing strategy, clinical characteristics were similar before and after allocation change. Subhazard models demonstrated reduced risk for waitlist mortality (p < .001) among each strategy except temporary VAD and increased transplantation rates (p < .001) among each strategy except for durable LVAD. These results validate the association of the new allocation system on waitlist outcomes across listing strategies.

Variation in additional testing and patient outcomes after stress echocardiography or myocardial perfusion imaging, according to accreditation status of testing site.

BACKGROUND: The purpose of the present study was to determine whether patients receiving a stress echocardiogram or myocardial perfusion imaging (MPI) test have differences in subsequent testing and outcomes according to accreditation status of the original testing facility. METHODS AND RESULTS: An all-payer claims dataset from Maine Health Data Organization from 2012 to 2014 was utilized to define two cohorts defined by an initial stress echocardiogram or MPI test. The accreditation status (Intersocietal Accreditation Commission (IAC), American College of Radiology (ACR) or none) of the facility performing the index test was known. Descriptive statistics and multivariate regression were used to examine differences in subsequent diagnostic testing and cardiac outcomes. We observed 4603 index stress echocardiograms and 8449 MPI tests. Multivariate models showed higher odds of subsequent MPI testing and hospitalization for angina if the index test was performed at a non-accredited facility in both the stress echocardiogram cohort and the MPI cohort. We also observed higher odds of percutaneous coronary interventions (PCI) performed (OR 1.68, 95% CI 1.13-2.50), if the initial MPI test was done in a non-accredited facility. CONCLUSION: Cardiac testing completed in non-accredited facilities were associated with higher odds of subsequent MPI testing, hospitalization for angina, and PCI.

Altered Sex Chromosome Dosage Induces Coordinated Shifts in Cortical Anatomy and Anatomical Covariance.

Sex chromosome dosage (SCD) variation increases risk for neuropsychiatric impairment, which may reflect direct SCD effects on brain organization. Here, we 1) map cumulative X- and Y-chromosome dosage effects on regional cortical thickness (CT) and investigate potential functional implications of these effects using Neurosynth, 2) test if this map is organized by patterns of CT covariance that are evident in health, and 3) characterize SCD effects on CT covariance itself. We modeled SCD effects on CT and CT covariance for 308 equally sized regions of the cortical sheet using structural neuroimaging data from 301 individuals with varying numbers of sex chromosomes (169 euploid, 132 aneuploid). Mounting SCD increased CT in the rostral frontal cortex and decreased CT in the lateral temporal cortex, bilaterally. Regions targeted by SCD were associated with social functioning, language processing, and comprehension. Cortical regions with a similar degree of SCD-sensitivity showed heightened CT covariance in health. Finally, greater SCD also increased covariance among regions similarly affected by SCD. Our study both 1) develops novel methods for comparing typical and disease-related structural covariance networks in the brain and 2) uses these techniques to resolve and identify organizing principles for SCD effects on regional cortical anatomy and anatomical covariance.

Sex-chromosome dosage effects on gene expression in humans.

A fundamental question in the biology of sex differences has eluded direct study in humans: How does sex-chromosome dosage (SCD) shape genome function? To address this, we developed a systematic map of SCD effects on gene function by analyzing genome-wide expression data in humans with diverse sex-chromosome aneuploidies (XO, XXX, XXY, XYY, and XXYY). For sex chromosomes, we demonstrate a pattern of obligate dosage sensitivity among evolutionarily preserved X-Y homologs and update prevailing theoretical models for SCD compensation by detecting X-linked genes that increase expression with decreasing X- and/or Y-chromosome dosage. We further show that SCD-sensitive sex-chromosome genes regulate specific coexpression networks of SCD-sensitive autosomal genes with critical cellular functions and a demonstrable potential to mediate previously documented SCD effects on disease. These gene coexpression results converge with analysis of transcription factor binding site enrichment and measures of gene expression in murine knockout models to spotlight the dosage-sensitive X-linked transcription factor ZFX as a key mediator of SCD effects on wider genome expression. Our findings characterize the effects of SCD broadly across the genome, with potential implications for human phenotypic variation.

Updated Analysis of the Oncology Section of the OITE from 2007 to 2019.

The Orthopaedic In-Training Exam (OITE) is administered annually to orthopedic surgery residents to assess their medical knowledge. The authors provide a comprehensive review of the orthopedic oncology portion of the exam in order to aid residents in preparation for future in-training and licensing examinations as well as to help guide oncology residency education curriculum. All of the orthopedic oncology questions on the OITE from 2007 to 2019 were reviewed. Analysis included (1) the number of oncology questions each year, (2) question topic, (3) question taxonomy (knowledge versus interpretation), (4) the type of imaging modalities (radiological, histological), (5) most commonly cited references, and (6) level of evidence. Descriptive statistics were utilized to compare means between variables. From 2007 to 2019, there was a total of 292 tumor-related questions with a mean of 22.5 tumor-related questions (range 19-28) per year. Of the questions, 54.8% pertained to malignant tumors and 45.2% to benign tumors. Assessment of question taxonomy showed that 79.8% of questions required interpretation of imaging and analysis of the information provided versus 20.2% of questions being knowledge recall type. Of the questions, 76.7% required interpretation of radiological images, pathological images, or both. Orthopaedic Knowledge Update, Journal of the American Academy of Orthopaedic Surgeons, and Journal of Bone and Joint Surgery were the three most commonly cited question sources. Only 29 (9.84%) oncology questions over the past 13 years have been supported by level I or II sources of evidence. Better understanding of the OITE make-up, question distribution, and number and style of question, reference sources can improve an orthopedic residents' performance as well as better guide educational curriculum to prepare residents in their orthopedic oncology education.

A Comprehensive Quantitative Genetic Analysis of Cerebral Surface Area in Youth.

The genetics of cortical arealization in youth is not well understood. In this study, we use a genetically informative sample of 677 typically developing children and adolescents (mean age 12.72 years), high-resolution MRI, and quantitative genetic methodology to address several fundamental questions on the genetics of cerebral surface area. We estimate that >85% of the phenotypic variance in total brain surface area in youth is attributable to additive genetic factors. We also observed pronounced regional variability in the genetic influences on surface area, with the most heritable areas seen in primary visual and visual association cortex. A shared global genetic factor strongly influenced large areas of the frontal and temporal cortex, mirroring regions that are the most evolutionarily novel in humans relative to other primates. In contrast to studies on older populations, we observed statistically significant genetic correlations between measures of surface area and cortical thickness (rG = 0.63), suggestive of overlapping genetic influences between these endophenotypes early in life. Finally, we identified strong and highly asymmetric genetically mediated associations between Full-Scale Intelligence Quotient and left perisylvian surface area, particularly receptive language centers. Our findings suggest that spatially complex and temporally dynamic genetic factors are influencing cerebral surface area in our species.SIGNIFICANCE STATEMENT Over evolution, the human cortex has undergone massive expansion. In humans, patterns of neurodevelopmental expansion mirror evolutionary changes. However, there is a sparsity of information on how genetics impacts surface area maturation. Here, we present a systematic analysis of the genetics of cerebral surface area in youth. We confirm prior research that implicates genetics as the dominant force influencing individual differences in global surface area. We also find evidence that evolutionarily novel brain regions share common genetics, that overlapping genetic factors influence both area and thickness in youth, and the presence of strong genetically mediated associations between intelligence and surface area in language centers. These findings further elucidate the complex role that genetics plays in brain development and function.

Imipenem-Relebactam Susceptibility Testing of Gram-Negative Bacilli by Agar Dilution, Disk Diffusion, and Gradient Strip Methods Compared with Broth Microdilution.

This study aimed to determine whether agar dilution, research-use-only disk diffusion (Mast Group Ltd., Bootle Merseyside, UK), Etest (bioMérieux, Inc., Durham, NC), and MIC test strip (MTS) (Liofilchem, Inc., Waltham, MA) methods yield equivalent results to those of broth microdilution (BMD) for imipenem-relebactam susceptibility testing using a collection of 297 Gram-negative bacilli, including members of the order Enterobacterales and Pseudomonas aeruginosa, enriched for drug resistance. MIC and disk diameter results were interpreted using United States Food and Drug Administration breakpoints. Overall, 76.8% of the isolates tested were susceptible to imipenem-relebactam by BMD. MIC values for agar dilution, Etest, and MTS were not significantly different from that for BMD, although they tended to be 1 to 2 dilutions higher. Essential agreement was 95.6% for agar dilution, 90.6% for Etest, and 85.2% for MTS. Categorical agreement was 98.0% for agar dilution, 73.1% for disk diffusion, 96.3% for Etest, and 96.6% for MTS. In conclusion, agar dilution and Etest yielded comparable results to BMD for imipenem-relebactam.

Nanoporous Thin Films Formed from Photocleavable Diblock Copolymers on Gold Substrates Modified with Thiolate Self-Assembled Monolayers.

Nanoporous thin films formed on electrodes are considered functional elements of electrochemical sensing systems, thus motivating methods for their development. We report a preparative strategy detailing the effects of surface modification of gold substrates with thiolate self-assembled monolayers (SAMs) on the properties of nanoporous thin films derived from polystyrene-block-poly(ethylene oxide) having a photocleavable o-nitrobenzyl ester junction (PS-hν-PEO). Two PS-hν-PEO having similar PEO volume fractions (≈0.2) but different molecular weights (10 and 23 kg/mol) were used to prepare films (30-100 nm thick) spin-cast on gold substrates unmodified and modified with cysteamine, thioctic acid, and 6-hydroxy-1-hexanethiol SAMs. Solvent vapor annealing followed by PEO removal led to the formation of nanopores with average diameters of 12 and 19 nm from the smaller and larger PS-hν-PEO, respectively. Cyclic voltammograms of 1,1'-ferrocenedimethanol showed that nanoporous films on cysteamine SAMs afforded nanopores reaching the underlying substrates at higher density than those on the other substrates. This result was attributed to balanced affinity of the cysteamine SAM surface with PS and PEO, which enhanced the vertical orientation of PEO microdomains. The generation of carboxyl groups associated with the photocleavage reaction was revealed by pH-dependent changes in the voltammogram of Fe(CN)63- that reflected electrostatic effects regulated by the protonation state of the carboxyl groups. The SAMs underneath the nanoporous films could be replaced by treatment with a thiol solution, as verified by voltammograms of l-ascorbic acid. These results suggest that thiolate SAM modification provides a simple means to control the interfacial orientation of PEO microdomains in thin PS-hν-PEO films.