Characterization of Pediatric Female Genital Trauma Using a Novel Grading System and Recommendations for Management.

BACKGROUND: There is no standardized grading system for pediatric female genital trauma (PFGT), so patients may have over-utilization of resources relative to injury severity. We described current treatment patterns and outcomes at a high-volume trauma center, developed a novel PFGT grading system, and proposed algorithm for management of PFGT. METHODS: We retrospectively reviewed female patients <19 years presenting with genital trauma to our Level 1 pediatric trauma center between 1/2018-12/2022. A novel grading system developed by pediatric surgery and pediatric gynecology was retrospectively applied to injuries. Patient demographics, injury characteristics, types of intervention, and need for anesthesia were recorded. Outcomes were compared between grades of injury with Kruskal-Wallis tests. RESULTS: Among 353 patients, median age was 6.4 years. Half of patients had grade 1 or 2 injuries, of which 6% required suture repair. 15% of patients had grade 5 or 6 injuries, 75% of whom required suture repair. General anesthesia was used for 83% of all patients undergoing repair. 18% of patients who underwent general anesthesia did not need suture repair. Of patients who were brought to the operating room, median operative duration varied by grade and was 15.0 min for all injuries, 7.0 min for both grade 1 and 2 injuries, and 22.0 and 37.0 min for grade 5 and 6 injuries, respectively (p < 0.0001). CONCLUSIONS: Based on our novel grading system, we propose an algorithm for managing PFGT. Grade 1 and 2 injuries rarely require suture repair and can often be managed without surgical consultation. We recommend surgical consultation for higher grade injuries, however given typically short operative times, repair with bedside sedation should be strongly considered when resources allow. LEVEL OF EVIDENCE: IV.

A Comparison of Racial and Ethnic Disparities in Complications Following Burn Injury in Adult Patients.

Burn injury contributes to significant morbidity and mortality in the United States. Despite an increased focus on racial and ethnic disparities in healthcare, there remains a critical knowledge gap in our understanding of the effect of these disparities on complications experienced by burn patients. The American Burn Association's National Burn Repository data were reviewed from 2010-2018. Information regarding demographics, burn mechanism and severity, complications, and clinical outcomes were recorded. Data analysis was performed using 1:1 propensity-score-matching and logistic regression modeling. A separate analysis of Hispanic and non-Hispanic patients was performed using Chi squared tests. Among 215,071 patients, racial distribution was 65.16% white, 19.13% black, 2.18% Asian, 0.74% American Indian/Alaskan Native, and 12.78% other. Flame injuries were the most common cause (35.2%), followed by scald burns (23.3%). All comparisons were made in reference to the white population. Black patients were more likely to die (OR: 1.28; 95%CI: 1.17-1.40), experience all (OR: 1.08; 95%CI: 1.03-1.14), cardiovascular (OR: 1.24; 95%CI: 1.08-1.43), or infectious (OR: 1.64; 95%CI: 1.40-1.91) complications, and less likely to experience airway complications (OR: 0.83; 95%CI: 0.74-0.94). American Indian/Alaskan Native patients were more likely to experience any complication (OR: 1.33; 95%CI: 1.05-1.70). All minority groups had increased length of hospital stay. Black, Asian, and other patients had longer length of ICU stay. Black patients had longer ventilator duration. Among 82,775 patients, 24,075 patients were identified as Hispanic and 58,700 as non-Hispanic. Statistically significant differences were noted between groups in age, TBSA, proportion of 2nd degree burn, and proportion of 3rd degree burn (p<0.01). These findings highlight the need for further work to determine the etiology of these disparities to improve burn care for all patients.

Association of initial assessment variables and mortality in severe pediatric traumatic brain injury.

Background: Predictive scales have been used to prognosticate long-term outcomes of traumatic brain injury (TBI), but gaps remain in predicting mortality using initial trauma resuscitation data. We sought to evaluate the association of clinical variables collected during the initial resuscitation of intubated pediatric severe patients with TBI with in-hospital mortality. Methods: Intubated pediatric trauma patients <18 years with severe TBI (Glasgow coma scale (GCS) score ≤8) from January 2011 to December 2020 were included. Associations between initial trauma resuscitation variables (temperature, pulse, mean arterial blood pressure, GCS score, hemoglobin, international normalized ratio (INR), platelet count, oxygen saturation, end tidal carbon dioxide, blood glucose and pupillary response) and mortality were evaluated with multivariable logistic regression. Results: Among 314 patients, median age was 5.5 years (interquartile range (IQR): 2.2-12.8), GCS score was 3 (IQR: 3-6), Head Abbreviated Injury Score (hAIS) was 4 (IQR: 3-5), and most had a severe (25-49) Injury Severity Score (ISS) (48.7%, 153/314). Overall mortality was 26.8%. GCS score, hAIS, ISS, INR, platelet count, and blood glucose were associated with in-hospital mortality (all p<0.05). As age and GCS score increased, the odds of mortality decreased. Each 1-point increase in GCS score was associated with a 35% decrease in odds of mortality. As hAIS, INR, and blood glucose increased, the odds of mortality increased. With each 1.0 unit increase in INR, the odds of mortality increased by 1427%. Conclusions: Pediatric patients with severe TBI are at substantial risk for in-hospital mortality. Studies are needed to examine whether earlier interventions targeting specific parameters of INR and blood glucose impact mortality.

Impact of laser treatment on hypertrophic burn scars in pediatric burn patients.

Paediatric patients with hypertrophic burn scars benefit from laser treatment, but this treatment's effectiveness on burn wounds stratified by specific body region and prior burn wound therapy has not been fully evaluated. We performed a single center retrospective study of pediatric burn patients, treated with fractional CO2, with or without pulse dye, laser between 2018-2022. We identified 99 patients treated with 332 laser sessions. Median age at the time of burn injury was 4.0 years (IQR 1.7, 10.0) and 7.1 years (IQR 3.6, 12.2) at the time of first laser treatment. In the acute setting, 55.2 % were treated with dermal substrate followed by autografting, 29.6 % were treated with dermal substrate alone, and 9.1 % underwent autografting alone. Most body regions showed improvement in modified Vancouver Scar Scale (mVSS) score with laser treatment. mVSS scores improved significantly with treatment to the anterior trunk (-1.18, p = 0.01), arms (-1.14, p = 0.003), and legs (-1.17, p = 0.015). Averaging all body regions, the mVSS components of pigmentation (-0.34, p < 0.001) and vascularity (-0.47, p < 0.001), as well as total score (-0.81, p < 0.001) improved significantly. Knowing the variable effectiveness of laser treatment in pediatric burn scars is useful in counseling patients and families pre-treatment.

Characterizing Delirium and Associated Risk Factors Using the Cornell Assessment of Pediatric Delirium Score in Pediatric Burn Patients.

Delirium is a syndrome of acute brain dysfunction with disturbance in consciousness and cognition that is increasingly recognized in critically ill pediatric patients. The Cornell Assessment of Pediatric Delirium (CAPD) tool is used to detect delirium in children of all ages and developmental stages in various hospital settings. To date, the incidence of delirium in the pediatric burn population has been poorly defined. In order to describe the incidence as well as risk factors for delirium in this patient population, we retrospectively reviewed patients <18 years of age admitted to our American Burn Association-verified pediatric burn center from March 2018 to May 2021 who underwent delirium screening using the CAPD tool. Patient demographics, burn characteristics, hospitalization details, and date of first positive delirium screening were collected, and χ2, Fisher's exact test, univariate, and multivariate analyses were performed. Delirium was identified in 42 (10.8%) of 389 patients meeting inclusion criteria. Patients screening positive for delirium were older (4 years [IQR: 2, 11] vs 2 years [IQR: 1, 6], P < .0005) and had larger TBSA burns (21.63% [IQR: 9, 42] vs 3.5% [IQR: 1.75, 6], P < .0001) than delirium-negative patients. Delirium-positive patients required a longer duration of mechanical ventilation (OR 4.23; 95% CI [1.16-15.39], P = .0289) and had higher TBSA burns (OR 1.12; 95% CI [1.06-1.17], P < .0001). Delirium-positive patients had 1.6 day longer length-of-stay adjusted for TBSA burned (95% CI [0.81-2.41], P < .0001). Compared to delirium-negative patients, delirium-positive patients had a 5.4-day longer PICU admission (95% CI [2.93-10.3]; P < .0001). Screening pediatric burn patients with risk factors known to be associated with delirium by using the CAPD score could improve delirium prevention and allow for early intervention.

A single institution case series of ReCell® use in treating pediatric burns.

BACKGROUND: Thermal injury has a significant impact on disability and morbidity in pediatric patients. Challenges in caring for pediatric burn patients include limited donor sites for large total body surface area (TBSA) burn as well as optimization of wound management for long term growth and cosmesis. ReCell® technology produces autologous skin cell suspensions from minimal donor split-thickness skin samples, allowing for expanded coverage using minimal donor skin. Most literature on outcomes reports on adult patients. OBJECTIVE: We present the largest to-date retrospective review of ReCell® technology use in pediatric patients at a single pediatric burn center. METHOD: Patients were treated at a quaternary care, free-standing, American Burn Association verified Pediatric Burn Center. A retrospective chart review was performed from September 2019 to March 2022, during which time twenty-one pediatric burn patients had been treated with ReCell® technology. Patient information was collected, including demographics, hospital course, burn wound characteristics, number of ReCell® applications, adjunct procedures, complications, healing time, Vancouver scar scale measurements, and follow-up. A descriptive analysis was performed, and medians were reported. RESULTS: Median TBSA burn on initial presentation was 31% (ranging 4%-86%). The majority of patients (95.2%) had placement of a dermal substrate prior to ReCell® application. Four patients did not receive split thickness skin grafting with their ReCell® treatment. The median time between date of burn injury and first ReCell® application was 18 days (ranging 5-43 days). The number of ReCell® applications ranged from 1-4 per patient. Median time until wound was classified as healed was 81 days (ranging 39-573 days). The median maximum Vancouver scar scale measurement per patient at time healed was 8, ranging from 3-14. Five patients who received skin grafts had graft loss and three of these patients had graft loss from areas with ReCell®. CONCLUSION: ReCell® technology provides an additional method for wound coverage, either on its own or in conjunction with split thickness skin grafting, and is safe and effective in pediatric patients.

Evaluating effects of burn injury characteristics on quality of life in pediatric burn patients and caregivers.

OBJECTIVES: The purpose of this study was to evaluate pediatric burn patients' and caregivers' quality of life (QoL), while identifying clinical characteristics correlated with psychological stress. METHODS: Pediatric burn patients at an ABA-verified institution from November 2019-January 2021 were included. Caregivers of patients 0-4 years completed the Infant's Dermatology QoL Index (IDQOL). Patients> 4-16 years completed the Children's Dermatology Life Quality Index (CDLQI). The Short Post-Traumatic Stress Disorder Rating Interview (SPRINT) measured caregivers' stress. Generalized linear mixed models evaluated associations between assessment scores and burn characteristics. RESULTS: Overall, 27.3% (39/143) of IDQOL and 53.1.% (41/96) of CDLQI scores indicated that patients' burns caused moderate to extremely large effects on QoL. In caregivers, 4.5% (7/159) scored> 14 on the SPRINT, warranting further PTSD evaluation. For the IDQOL, each additional 1% TBSA burn was associated with a 2.75-point increase (p = 0.05), and patients sustaining 2nd degree deep partial thickness burns scored an average of 3.3 points higher compared to 2nd degree superficial partial thickness burns (P < 0.01). CLDQI and SPRINT scores demonstrated a similar pattern. CONCLUSIONS: QoL is impacted in a substantial proportion of pediatric burn patients. Larger TBSA and increased burn depths cause significantly more psychological stress in children, and caregivers may require more extensive psychological evaluation.

Dermal substrate application in the treatment of pediatric hand burns: clinical and functional outcomes.

BACKGROUND: Hand burn injuries are common among pediatric patients. Management of deep partial thickness and full thickness hand burns varies by center, with some favoring upfront autografting and others using dermal substrates (DS) as biologic dressings to accelerate burn wound healing. Achieving best outcomes is critical in children given the propensity of burn wound scars to affect hand function as a child grows and develops. Given potential complications associated with autografting in children, our center often prefers to treat pediatric hand burns initially with DS, with subsequent autografting if there is failure to heal. In this case series, we examined the outcomes of this practice. METHODS: We conducted a retrospective review of pediatric burn patients with <10% total body surface area (TBSA) burns who underwent application of DS to hand burn injuries between 2013 and 2021. Burn mechanism, patient demographics, wound treatment details, healing and functional outcomes, and complications were collected. Descriptive statistics were computed. RESULTS: Fifty patients with hand burns and overall <10% TBSA burns underwent application of DS to hands. Median age at the time of injury was 4.1 years (IQR: 1.8, 10.7) and 29 patients (58%) were male. Eighteen (36%) patients had bilateral hand burns, 10 (20%) had burns to their dominant hand, 6 (12%) their non-dominant hand, and 16 (32%) had unestablished or unknown hand dominance. Subsequent autografting was required in 5 (10%) patients treated initially with DS; four of these patients had full thickness injuries. Five (10%) patients developed contracture at the site of DS application for which two underwent scar release with tissue rearrangement, one underwent laser treatment, and two were managed conservatively. Most patients had splints (94%), or compression garments (54%) prescribed to aid in functional recovery. CONCLUSION: Children with hand burns who underwent DS application healed well with few requiring autografting or developing contractures. Most patients who needed autografting had deeper injuries. Most patients who developed a contracture required additional procedural intervention. Recognizing factors that contribute to the need for autografting after initial treatment with DS can help direct intervention decisions in pediatric patients with hand burn injuries.

Length of Stay Per Total Body Surface Area Burn: A Validation Study Using the National Burn Registry.

A length of stay (LOS) of one day per percent total body surface area (TBSA) burn has been generally accepted but not validated in current pediatric burn studies. The primary objective of this study is to validate previous Pediatric Injury Quality Improvement Collaboration (PIQIC) findings by using a national burn registry to evaluate LOS per TBSA burn relative to burn mechanism, sociodemographic characteristics, and clinical factors which influence this ratio. We evaluated patients 0-18 years old who sustained a burn injury and whose demographics were submitted to the National Burn Registry (NBR) dataset from July 2008 through June 2018. Mixed effects generalized additive regression models were performed to identify characteristics associated with the LOS per TBSA burn ratio. Among 51,561 pediatric burn patients, 45% were Non-Hispanic White, 58% were male, and median age was 3.0 years old (IQR: 1.0, 9.0). The most common burn mechanism was scald (55.9%). The median LOS per TBSA burn ratio across all cases was 0.9 (IQR: 0.4, 1.75). In adjusted models, scald burns had a mean predicted LOS per TBSA burn value of 1.2 while chemical burns had the highest ratio (4.8). Non-Hispanic White patients had lower LOS per TBSA burn ratios than all other races and ethnicities (p < .05). These data substantiate evidence on variance in LOS per TBSA burn relative to burn mechanism and race/ethnicity. Knowing these variations can guide expectations in hospital LOS for patients and families and help burn centers benchmark their clinical performance.

"Yes, I'm the Doctor": One Department's Approach to Assessing and Addressing Gender-Based Discrimination in the Modern Medical Training Era.

While gender-based bias and discrimination (GBD) is known to exist in medical training, there is limited guidance for training programs on how to understand and combat this issue locally. The Massachusetts General Hospital Department of Surgery established the Gender Equity Task Force (GETF) to address GBD in the local training environment. In 2017, members of the GETF surveyed residents in surgery, anesthesia, and internal medicine at 2 academic hospitals to better understand perceived sources, frequency, forms, and effects of GBD. Overall, 371 residents completed the survey (60% response rate, 197 women). Women trainees were more likely to endorse personal experience of GBD and sexual harassment than men (P < .0001), with no effect of specialty on rates of GBD or sexual harassment. Patients and nursing staff were the most frequently identified groups as sources of GBD. While an overwhelming majority of both men (86%) and women (96%) respondents either experienced or observed GBD in the training environment, less than 5% of respondents formally reported such experiences, most frequently citing a belief that nothing would happen. Survey results served as the basis for a variety of interventions addressing nursing staff and patients as sources of GBD, low confidence in formal reporting mechanisms, and the pervasiveness of GBD, including sexual harassment, across specialties. These results reproduce other studies' findings that GBD and sexual harassment disproportionately affect women trainees while demonstrating how individual training programs can incorporate local GBD data when planning interventions to address GBD.

Bioengineering of functional human induced pluripotent stem cell-derived intestinal grafts.

Patients with short bowel syndrome lack sufficient functional intestine to sustain themselves with enteral intake alone. Transplantable vascularized bioengineered intestine could restore nutrient absorption. Here we report the engineering of humanized intestinal grafts by repopulating decellularized rat intestinal matrix with human induced pluripotent stem cell-derived intestinal epithelium and human endothelium. After 28 days of in vitro culture, hiPSC-derived progenitor cells differentiate into a monolayer of polarized intestinal epithelium. Human endothelial cells seeded via native vasculature restore perfusability. Ex vivo isolated perfusion testing confirms transfer of glucose and medium-chain fatty acids from lumen to venous effluent. Four weeks after transplantation to RNU rats, grafts show survival and maturation of regenerated epithelium. Systemic venous sampling and positron emission tomography confirm uptake of glucose and fatty acids in vivo. Bioengineering intestine on vascularized native scaffolds could bridge the gap between cell/tissue-scale regeneration and whole organ-scale technology needed to treat intestinal failure patients.There is a need for humanised grafts to treat patients with intestinal failure. Here, the authors generate intestinal grafts by recellularizing native intestinal matrix with human induced pluripotent stem cell-derived epithelium and human endothelium, and show nutrient absorption after transplantation in rats.

Spray Delivery of Intestinal Organoids to Reconstitute Epithelium on Decellularized Native Extracellular Matrix.

The native extracellular matrix (ECM) serves as a unique platform for tissue engineering because it provides an organ-specific scaffold in terms of both matrix composition and tissue architecture. However, efficacious cell-seeding techniques for recellularizing the ECM constructs with appropriate cell types to restore biological function remain under development. In this study, the impact of spraying as a seeding technique for repopulation of decellularized small intestine was investigated. In a series of experiments, CaCo-2 cells were first used to investigate the effect of spray device type and pressure on cell viability and to optimize parameters for seeding intestinal epithelial cells. High cell viability and a homogeneous cell distribution were obtained when cell suspensions were sprayed through an airbrush at low pressure. Next, the effect of seeding method and spray pressure on the size and dispersal of intestinal organoids, a more complex and clinically relevant intestinal stem cell population, was evaluated. The feasibility of seeding intestinal epithelial cells onto decellularized scaffolds was next studied using sprayed CaCo-2 cells, which survived the spray-seeding process and formed a monolayer on the scaffold. Finally, airbrush seeding was used to spray intestinal organoids onto the scaffolds, with cell survival and tissue architecture evaluated after 1 week of culture. Organoids seeded through pipetting onto the decellularized scaffold survived, but demonstrated aggregation, with cells organized around multiple small lumens. In contrast, organoids airbrush spray seeded at 0.35 bar onto the decellularized scaffold not only engrafted but also demonstrated formation of an epithelial monolayer that resembled the absorptive surface found on intestinal villi. The results suggest that seeding cells through airbrush spraying holds great potential for use in tissue engineering, especially for large-scale tubular organ recellularization.

Unusual Breast Calcifications: Complete Replacement of Fibroglandular Tissue with Dystrophic Calcifications in End-Stage Renal Disease.

We present a rare case of breast calcifications in a patient with end-stage renal disease (ESRD) who was noncompliant with peritoneal dialysis. She presented with rapid onset of a palpable breast mass. Breast ultrasound (US) demonstrated ill-defined areas of dense tissue in the breasts bilaterally. Mammography demonstrated coarse, branching calcifications, completely replacing normal fibroglandular tissue. A review of the literature yields one similar case. The current hypothesis for patients with increased breast calcifications includes elevated serum calcium, phosphate, and parathyroid hormone (PTH) levels; calcium phosphate products may be critical to calcification in ESRD. However, our patient presented with low-normal serum calcium and phosphate, suggesting that this rare entity of breast calcifications is probably related to other unknown factors.

Bowel dysfunction following pullthrough surgery is associated with an overabundance of nitrergic neurons in Hirschsprung disease.

PURPOSE: Recent evidence suggests that patients with Hirschsprung disease (HD) have abnormal neurotransmitter expression in the ganglionated proximal colon. These alterations may cause persistent bowel dysfunction even after pullthrough surgery. We sought to quantify the proportion of nitrergic neurons in the ganglionic colon of HD patients and relate these findings to functional outcome. METHODS: The proximal resection margin from 17 patients with colonic HD who underwent a pullthrough procedure and colorectal tissue from 4 age-matched controls were immunohistochemically examined to quantify the proportion of nitrergic neurons. The incidence of constipation, incontinence, and enterocolitis in HD patients was assessed retrospectively and correlated with the proportion of nitric oxide synthase (NOS) expressing neurons. Neuronal subtypes in the ganglionic colon of the Edrnb-/- mouse model of HD were also studied. RESULTS: Mice with HD had a significantly higher proportion of NOS+ neurons in ganglionic colon than normal littermates (32.0±5.6% vs. 19.8±1.2%, p<0.01). Patients with HD also had significantly more NOS+ neurons than controls (18.4±4.6% vs. 13.1±1.9%, p<0.01). Patients who experienced constipation or enterocolitis postoperatively tended toward a higher proportion of NOS+ neurons (21.4±3.9% vs. 17.1±4.1%, p=0.06). Furthermore, patients with a proportion of NOS+ neurons above the median of all HD patients (18.3%) were significantly more likely to have constipation than those below the median (75% vs. 14%, p<0.05). CONCLUSION: An overabundance of nitrergic neurons in the proximal resection margin is associated with HD and may predict bowel dysfunction following pullthrough surgery.

Are abusive fractures in young children becoming less common? Changes over 24 years.

OBJECTIVE: To determine whether the proportion of fractures rated as abusive in children <36 months of age evaluated at a regional pediatric hospital increased over a 24-year period from 1979 to 2002. Fractures were chosen as an example of serious injuries in young children. METHODS: Medical records were abstracted for all children <36 months of age who were seen at a single pediatric hospital with a fracture during three time periods: 1979-1983, 1991-1994, and 1999-2002. After reviewing the abstracted and radiographic information, two clinicians (one an expert on child abuse) and two pediatric radiologists each rated the likelihood of abuse using explicit criteria and a seven-point scale from definite abuse to definite unintentional injury. Ratings were done independently; when disagreements occurred, the case was discussed, and a joint rating was agreed upon, if possible. The proportions of cases rated as abuse were compared over the three time periods, and logistic regression was used to calculate adjusted odds ratios (OR). RESULTS: In the early, middle, and late samples, there were 200, 240, and 232 children, respectively, with fractures. The proportion of cases rated as abuse decreased from 22.5% in the early period to 10.0% in the middle period and was 10.8% in the late period (p<.001). When comparing the odds of abuse in the middle and late groups to the odds of abuse in the early group (controlling for age, gender, ethnicity, type of medical insurance, and site of pediatric care), the adjusted ORs were .31 (95% CI=.15, .62) for the middle group and .45 (95% CI=.23, .86) for the late group. Thus, the odds of a given case being rated as abuse decreased by over 50% from the early period to the middle and late time periods. No statistically significant difference was found when comparing the odds of abuse for the middle group to those of the late group, OR: 1.46 (95% CI=.69, 3.08). CONCLUSIONS: The proportion of abusive fractures in young children decreased substantially from 1979-1983 to 1991-1994 and 1999-2002 at a major pediatric hospital. We speculate that this decrease may reflect early recognition of less serious forms of maltreatment and the availability of services to high-risk families.

Direct kinetic correlation of carriers and ferromagnetism in Co2+: ZnO.

The hypothesis that high-Curie-temperature ferromagnetism in cobalt-doped ZnO (Co2+: ZnO) is mediated by charge carriers was tested by controlled introduction and removal of the shallow donor interstitial zinc. Using oriented epitaxial Co2+: ZnO films grown by chemical vapor deposition, kinetics measurements demonstrate a direct correlation between the oxidative quenching of ferromagnetism and the diffusion and oxidation of interstitial zinc. These results demonstrate controlled systematic variation of a key parameter involved in the ferromagnetism of Co2+: ZnO and, in the process, unambiguously reveal this ferromagnetism to be dependent upon charge carriers. The distinction between defect-bound and free carriers in Co2+: ZnO is discussed.

The influence of dopants on the nucleation of semiconductor nanocrystals from homogeneous solution.

The influence of Co2+ ions on the homogeneous nucleation of ZnO is examined. Using electronic absorption spectroscopy as a dopant-specific in-situ spectroscopic probe, Co2+ ions are found to be quantitatively excluded from the ZnO critical nuclei but incorporated nearly statistically in the subsequent growth layers, resulting in crystallites with pure ZnO cores and Zn(1-x)Co(x)O shells. Strong inhibition of ZnO nucleation by Co2+ ions is also observed. These results are explained using the classical nucleation model. Statistical analysis of nucleation inhibition data allows estimation of the critical nucleus size as 25 +/- 4 Zn2+ ions. Bulk calorimetric data allow the activation barrier for ZnO nucleation containing a single Co2+ impurity to be estimated as 5.75 kcal/mol cluster greater than that of pure ZnO, corresponding to a 1.5 x 10(4)-fold reduction in the ZnO nucleation rate constant upon introduction of a single Co2+ impurity. These data and analysis offer a rare view into the role of composition in homogeneous nucleation processes, and specifically address recent experiments targeting formation of semiconductor quantum dots containing single magnetic impurity ions at their precise centers.

Synthesis of colloidal Mn2+:ZnO quantum dots and high-TC ferromagnetic nanocrystalline thin films.

We report the synthesis of colloidal Mn(2+)-doped ZnO (Mn(2+):ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn(2+):ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)(2) was found to strongly inhibit oxidation of Mn(2+) by O(2), allowing the synthesis of Mn(2+):ZnO to be performed aerobically. Mn(2+) ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn(2+):ZnO colloids of nearly spherical shape and uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn(2+) with very homogeneous speciation, differing from bulk Mn(2+):ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin-coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 micro(B)/Mn(2+) and T(C) > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn(2+):ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.