Anatomy Camp: A Medical Student-Run Outreach Program.

Anatomy Camp is a medical student-run program for underserved youth from communities near the university. Middle and high school students are invited to visit the medical school for an afternoon of interacting with medical students, informal learning of anatomy and wellness, and becoming inspired to consider medical and STEM professions.

Ionic Liquid-Assisted Thermal Evaporation of Bimetallic Ag-Au Nanoparticle Films as a Highly Reproducible SERS Substrate for Sensitive Nanoplastic Detection in Complex Environments.

Nanoplastic particles are emerging as an important class of environmental pollutants in the atmosphere that have adverse effects on our ecosystems and human health. While many methods have been developed to quantitatively detect nanoplastics; however, sensitive detection at low concentrations in a complex environment remains elusive. Herein, we demonstrate a greener method to fabricate a surface-enhanced Raman spectroscopy (SERS) substrate consisting of self-assembled plasmonic Ag-Au bimetallic nanoparticle (NP) films for quantitative SERS detection of nanoplastics in complex media. The self-assembly of Ag-Au bimetallic NPs was achieved through thermal evaporation onto a vapor-phase compatible ionic liquid based on deep eutectic solvent over the growth substrate. The finite-difference time-domain simulation revealed that the localized field enhancement is strong in the gaps, which generate uniform SERS "hotspots" in the obtained substrate. Benefiting from highly accessible SERS "hotspots" at the gaps, the SERS substrate exhibits excellent sensitivity for detecting crystal violet with a limit of detection (LOD) as low as 10-14 M and excellent reproducibility (RSD of 5.8%). The SERS substrate is capable of detecting PET nanoplastics with LOD as low as 1 µg/mL and about 100 µg/mL in real samples such as tap water, lake water, diluted milk, and wine. Moreover, we also validated the feasibility of the designed SERS substrate for the practical detection of PET nanoplastics collected from commercial drinking water bottles, and it showed great potential applications for sensitive detection in actual environments.

Recent Progress in Retinal Pigment Epithelium Cell-Based Therapy for Retinal Disease.

Age-related macular degeneration and retinitis pigmentosa are degenerative retinal diseases that cause severe vision loss. Early clinical trials involving transplantation of retinal pigment epithelial cells and/or photoreceptors as a treatment for these conditions are underway. In this review, we summarize recent progress in the field of retinal pigment epithelium transplantation, including some pertinent clinical trial results as well as preclinical studies that address issues of transplant immunology, cell delivery, and cell manufacturing.

Recent Progress in Photoreceptor Cell-Based Therapy for Degenerative Retinal Disease.

Age-related macular degeneration and retinitis pigmentosa are degenerative retinal diseases that cause severe vision loss. Early clinical trials involving transplantation of photoreceptors as treatment for these conditions are underway. In this review, we summarize recent progress in the field of photoreceptor transplantation, including some pertinent results regarding photoreceptor manufacture, photoreceptor transplantation, mechanisms of donor-host cell integration such as material transfer and photoreceptor transplant immunology. We conclude by proposing several approaches that may provide a rational basis for selecting a vision restoration strategy (eg, donor-host synapse formation vs donor-host nanotube formation) and improved transplant efficiency.

Unilateral acute iris transillumination syndrome with glaucoma and iris pigment epithelium dispersion simulating iris melanoma.

Purpose: To report a patient with a unilateral presentation of glaucoma, pain, and acute iris transillumination syndrome simulating iris melanoma. Observations: A 53-year-old male presented with blurred vision and pain in his right eye several weeks following a respiratory sinus infection managed by oral azithromycin. Examination of the right eye was notable for elevated intraocular pressure of 46 mm Hg, an irregular mid-dilated pupil, and diffuse iris transillumination with pigmentary seeding on the iris surface, in the anterior chamber angle, and on the sclera, suspicious for diffuse iris melanoma with glaucoma and extrascleral extension. Ultrasound biomicroscopy (UBM) of the right eye revealed circumferential anterior chamber angle and trabecular meshwork involvement by an infiltrative process corresponding to the pigmented cells noted clinically, while the ciliary body was unremarkable. Following enucleation, histopathology showed extensive necrosis of the iris pigment epithelium, sphincter, and dilator muscles with melanophagic infiltration in the anterior chamber angle and episclera, mild chronic non-granulomatous iridocyclitis, and no evidence of a melanocytic neoplasm. Although immunohistochemical studies for herpes simplex virus (HSV) types 1 and 2, varicella-zoster virus, and cytomegalovirus were negative, qualitative real-time polymerase chain reaction on paraffin-embedded tissue detected HSV-1 DNA. The combined clinical, pathologic, and molecular findings were compatible with unilateral acute iris transillumination syndrome, likely HSV-1 associated. Conclusion and Importance: Unilateral acute iris transillumination syndrome with diffuse iris pigment epithelial loss can simulate iris melanoma. Prompt herpes viral studies may be informative.

Adjuvant Intravitreal Bevacizumab for Retinal Neovascularization in Eales' Disease Associated With Latent Mycobacterium Tuberculosis.

We report a case of bilateral Eales' disease managed with intravitreal bevacizumab. A 32-year-old woman with a history of bacillus Calmette-Guerin vaccine, administered when she was 10 years old, presented with a five-day history of a scotoma in the temporal field of her right eye. A dilated fundus exam and fluorescein angiography showed bilateral retinal peripheral capillary non-perfusion, retinal neovascularization in the right eye, and deep intraretinal hemorrhages in the left eye. Her laboratory workup resulted in a positive QuantiFERON-TB Gold test (Cellestis Ltd, Carnegie, Victoria, Australia). Chest computed tomography showed a calcified granuloma in her right lung. Angiographic-guided pan-retinal photocoagulation was performed, and intravitreal injections of bevacizumab (1.25 mg/0.05 mL) were administered in both eyes over the course of three months. The intraretinal hemorrhages resolved after three months of therapy. Three months following treatment, the patient showed normal fundus findings without any evidence of recurrence and a visual acuity of 20/20 in both eyes. Intravitreal bevacizumab in combination with angiography-guided pan-retinal photocoagulation may be efficacious in select patients with Eales' disease.

Intravitreal Bevacizumab for Choroidal Neovascular Membrane in Macular Telangiectasia Type 2.

We report a case of macular telangiectasia type 2 with an associated choroidal neovascular membrane and its treatment. A 54-year-old female presented with a history of gradual vision loss in both eyes. A physical exam showed visual acuity of 20/40 in both eyes and significant metamorphopsia in the right eye. A fundus examination of the right eye was remarkable for right-angled vessels in the juxtafoveal region and subretinal fibrosis temporal to the fovea. A fundus examination of the left eye revealed intraretinal crystals in the juxtafoveal region and right-angled vessels. Optical coherence tomography and angiography confirmed the diagnosis of macular telangiectasia type 2 as well as the presence of a choroidal neovascular membrane in the right eye. The patient was treated with 18 intravitreal injections of anti-vascular endothelial growth factor agent in the right eye for two years, with five to six weeks between each treatment, which resulted in the membrane's stability. Our report suggests that anti-vascular endothelial growth factor therapy via intravitreal injection may be beneficial in treating choroidal neovascular membranes in patients with macular telangiectasia type 2.

Consultations in Eye Pathology: Experience at the Ophthalmology Specialty Hospital.

CONTEXT.­: Ophthalmic pathology is a discipline that relies heavily on a knowledge of clinical ophthalmology. The diagnosis of ocular and periocular lesions can be challenging because some lesions and diseases are unique to this region, whereas others may demonstrate site-specific differences from nonocular counterparts. Because of these challenges, ocular and periocular biopsies are frequently referred to specialized ophthalmic pathology centers for second opinion diagnoses. OBJECTIVE.­: To analyze the referral patterns, diagnostic challenges, and diagnostic discrepancies for second opinion referrals at a dedicated ophthalmic pathology laboratory with an emphasis on lesions of special interest in ophthalmic pathology. DATA SOURCES.­: Data sources included the pathology records of all slides and blocks received in consultation at the referral eye pathology center between December 1, 2015, and December 1, 2022, the personal experience of senior authors, and published peer-reviewed literature. CONCLUSIONS.­: Corneal, intraocular, and conjunctival biopsies are the most common types of cases received in consultation without the referring pathologist's diagnosis, likely reflecting diagnostic challenges. Degenerative intraocular processes occasionally raise concern for a neoplasm. Conjunctival melanocytic lesions are the most common conjunctival biopsies referred for second opinion diagnosis and require careful tissue sampling and clinical-pathologic correlation. Careful clinical-pathologic correlation, a high level of suspicion, and adequate sampling also are required for the accurate diagnosis of periocular sebaceous carcinoma. The diagnostic discrepancies involving uveal, retinal, conjunctival, eyelid, and temporal artery biopsies are most likely to adversely influence patient management and possible outcome. Such specimens may benefit from referral to specialized ophthalmic pathology laboratories.

Linfadenectomía mediastinal por muestreo vs. linfadenectomía completa en el cáncer pulmonar / Sampling Mediastinal Lymphadenectomy versus Complete Lymphadenectomy in Lung Cancer

Introducción: El muestreo y la linfadenectomía completa son técnicas de acceso al mediastino. Su evaluación permite definir la conducta en el enfermo con cáncer del pulmón. Objetivo: Determinar los resultados de supervivencia en los enfermos con lesiones resecables por cáncer de pulmón con linfadenectomía completa o linfadenectomía por muestreo. Métodos: Se realizó un estudio longitudinal tipo serie de casos en 118 pacientes con lesiones resecables de cáncer de pulmón de células no pequeñas. El total de pacientes se subdividieron en dos grupos. A los 73 enfermos pertenecientes al grupo A se les realizó linfadenectomía por muestreo (1996-2010), mientras que a los 45 del grupo B se les realizó linfadenectomía completa (2011-2019). Se analizaron las complicaciones y la supervivencia a los cinco años. Resultados: Se resecaron mayor cantidad de ganglios por paciente y por regiones en la linfadenectomía completa, con una supervivencia de 50,6 por ciento, superior al 39,7por ciento obtenido en el grupo donde se realizó un muestreo. No se recogieron complicaciones inherentes a las técnicas quirúrgicas. Conclusiones: Los pacientes operados con resección y linfadenectomía completa tuvieron mayor sobrevida que los intervenidos mediante resección y linfadenectomía por muestreo(AU)

Introduction: Sampling or complete lymphadenectomy are techniques for accessing the mediastinum. Their assessment allows to define the approach in patients with lung cancer. Objective: To determine survival outcomes in ill patients with resectable lesions due to lung cancer after complete or sampling lymphadenectomies. Methods: A longitudinal case series study was performed in 118 patients with resectable lesions of nonsmall-cell lung cancer. All the patients were divided into two groups. The 73 ill patients from group A underwent sampling lymphadenectomy (1996-2010), while the 45 patients from group B underwent complete lymphadenectomy (2011-2019). Complications and five-year survival were analyzed. Results: A higher amount of nodes were resected per patient and per region in complete lymphadenectomy, with a survival of 50.6 por ciento, higher than the 39.7 por ciento corresponding to the sampling group. No complications inherent to the surgical techniques were collected. Conclusions: Patients operated on by resection and complete lymphadenectomy had higher survival figures than those operated on by resection and sampling lymphadenectomy(AU)

Identification of the Vibrational Optical Coherence Tomography Corneal Cellular Peak.

Purpose: Our team previously identified the presence of five corneal resonant frequency (RF) peaks in healthy volunteers using vibrational optical coherence tomography (VOCT). Prior studies have suggested that the ≤100 Hz RF peak represents the cellular element of tissue. The aim of this study was to confirm that this peak reflects the human corneal cellular component using VOCT and histological analysis. Methods: Two human research globes were obtained from the same donor, and VOCT measurements were collected from the full-thickness corneas. A microkeratome was then used to create serial-free corneal caps from each cornea, with VOCT performed on the residual stromal bed after each excision. All lamellar sections from both globes were sent for histological analysis to determine cellularity. Cell counts on the specimens were performed by two independent observers. Results: The average of the normalized ≤100 Hz peak values before lamellar sectioning was significantly higher than the average of this peak values after the first, second, and third cuts (P = 0.023), which was 33.9% less than before any cuts. The cell count values in the first slice were significantly higher than the average cell count values of the three deeper slices (P < 0.001), and the cell count dropped 84.4% after the first slice was removed. Conclusions: The findings of this study suggest that the ≤100 Hz corneal peak identified by VOCT corresponds to the cellular component of the cornea. Translational Relevance: This work furthers our understanding of the origin of the corneal ≤100 Hz peak identified using VOCT.

Characteristics Upon Presentation of Patients with Type 2 Macular Telangiectasia in Puerto Rico.

OBJECTIVE: To describe the systemic disease associations and clinical features upon initial presentation of a cohort of patients with type 2 macular telangiectasia who live in Puerto Rico. METHODS: A retrospective review of patients with macular telangiectasia was performed in 4 private retina practices in Puerto Rico. The demographic and clinical characteristics were recorded. RESULTS: Twenty-one patients who were diagnosed with macular telangiectasia were included in the analysis. The median age of presentation was 62 years; 86% were female, and all patients were Hispanics. The median visual acuity at presentation was 20/50. A prior medical diagnosis of type II diabetes mellitus was found in 15 (71.4%) patients, essential hypertension in 12 (57.1%), and dyslipidemia in 9 (42.9%). All patients had bilateral disease. The most common ocular findings were the presence of right-angle vessels in 32 (76.2%) eyes and angiographic hyperfluorescence temporal to the fovea, found in 22 (52.4%) of the affected eyes. One eye had evidence of choroidal neovascularization. CONCLUSION: Our cohort showed a higher prevalence of type 2 diabetes in patients with type 2 macular telangiectasia than in other cohorts. It also supports the findings of other studies showing that macular telangiectasia patients are more likely to have type 2 diabetes and hyperlipidemia. However, the increased prevalence of diabetes and hyperlipidemia may be due to selection bias, and further studies are needed to assess the significance of these findings.

Abdomen agudo por vesícula biliar duplicada y complicada

RESUMEN Introducción: Las malformaciones de la vía biliar son extremadamente infrecuentes y en muchas ocasiones son un hallazgo en el acto quirúrgico. Cuando se presenta, el cuadro clínico es similar al del paciente que tiene vesícula sin malformaciones congénitas. Objetivo: Describir un caso de abdomen agudo por duplicidad de vesícula biliar complicada. Caso clínico: Paciente de 46 años, antecedentes de dispepsias, que acudió al cuerpo de guardia con dolor abdominal agudo. Se diagnostica gangrena vesicular y se decide tratamiento quirúrgico. En el transoperatorio, se constató doble sistema vesicular, uno con zona de necrosis y el otro con cambios inflamatorios crónicos. Se realiza colecistectomía a ambos órganos. La evolución fue favorable. Conclusiones: La ocurrencia de un abdomen agudo en un paciente con duplicidad vesicular es infrecuente. Se presenta el caso pues contribuye a profundizar en el conocimiento sobre la conducta a seguir en esta enfermedad.

ABSTRACT Introduction: Bile duct malformations are extremely rare, and generally do not present complications that justify urgent surgical intervention. When it occurs, the clinical picture is similar to that of a patient with a gallbladder without congenital malformations. Objective: Describe a case of acute abdomen due to complicated gallbladder duplication. Clinical case: 46-year-old patient with a history of dyspepsia, who came the emergency with acute abdominal pain. Gallbladder gangrene is diagnosed, and surgical treatment is decided. During surgery, a double vesicular system was found, one area of ​​necrosis and the other with chronic inflammatory changes. Cholecystectomy is performed on both organs. The evolution was favorable. Conclusions: The occurrence of an acute abdomen in a patient with gallbladder duplication is infrequent. The case is presented that contributes to deepen the knowledge about the course of action in this disease.

Insight into the molecular basis of substrate recognition by the wall teichoic acid glycosyltransferase TagA.

Wall teichoic acid (WTA) polymers are covalently affixed to the Gram-positive bacterial cell wall and have important functions in cell elongation, cell morphology, biofilm formation, and ß-lactam antibiotic resistance. The first committed step in WTA biosynthesis is catalyzed by the TagA glycosyltransferase (also called TarA), a peripheral membrane protein that produces the conserved linkage unit, which joins WTA to the cell wall peptidoglycan. TagA contains a conserved GT26 core domain followed by a C-terminal polypeptide tail that is important for catalysis and membrane binding. Here, we report the crystal structure of the Thermoanaerobacter italicus TagA enzyme bound to UDP-N-acetyl-d-mannosamine, revealing the molecular basis of substrate binding. Native MS experiments support the model that only monomeric TagA is enzymatically active and that it is stabilized by membrane binding. Molecular dynamics simulations and enzyme activity measurements indicate that the C-terminal polypeptide tail facilitates catalysis by encapsulating the UDP-N-acetyl-d-mannosamine substrate, presenting three highly conserved arginine residues to the active site that are important for catalysis (R214, R221, and R224). From these data, we present a mechanistic model of catalysis that ascribes functions for these residues. This work could facilitate the development of new antimicrobial compounds that disrupt WTA biosynthesis in pathogenic bacteria.

Small RNAs as a New Platform for Tuning the Biosynthesis of Silver Nanoparticles for Enhanced Material and Functional Properties.

Genetic engineering of nanoparticle biosynthesis in bacteria could help facilitate the production of nanoparticles with enhanced or desired properties. However, this process remains limited due to the lack of mechanistic knowledge regarding specific enzymes and other key biological factors. Herein, we report on the ability of small noncoding RNAs (sRNAs) to affect silver nanoparticle (AgNP) biosynthesis using the supernatant from the bacterium Deinococcus radiodurans. Deletion strains of 12 sRNAs potentially involved in the oxidative stress response were constructed, and the supernatants from these strains were screened for their effect on AgNP biosynthesis. We identified several sRNA deletions that drastically decreased AgNP yield compared to the wild-type (WT) strain, suggesting the importance of these sRNAs in AgNP biosynthesis. Furthermore, AgNPs biosynthesized using the supernatants from three of these sRNA deletion strains demonstrated significantly enhanced antimicrobial and catalytic activities against environmentally relevant dyes and bacteria relative to AgNPs biosynthesized using the WT strain. Characterization of these AgNPs using electron microscopy (EM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) revealed that the deletion of these small RNAs led to changes within the supernatant composition that altered AgNP properties such as the surface chemistry, surface potential, and overall composition. Taken together, our results demonstrate that modulating specific sRNA levels can affect the composition of supernatants used to biosynthesize AgNPs, resulting in AgNPs with unique material properties and improved functionality; as such, we introduce sRNAs as a new platform for genetically engineering the biosynthesis of metal nanoparticles using bacteria. Many of the sRNAs examined in this work have potential regulatory roles in oxidative stress responses; further studies into their targets could help provide insight into the specific molecular mechanisms underlying bacterial biosynthesis and metal reduction, enabling the production of nanoparticles with enhanced properties.

Osteosíntesis mínima invasiva percutánea con placa en fractura de tibia distal / Percutaneous Minimally Invasive Plate Osteosynthesis in Distal Tibial Fracture

Introducción: Las fracturas diafisarias de la tibia tienen una alta incidencia por año, incluidas las del tercio distal. Son las más frecuentes de los huesos largos y se observan sobre todo en adultos jóvenes. Se producen, generalmente, por traumatismos de alta energía como accidentes del tránsito y caídas de alturas. Objetivo: Presentar los resultados del tratamiento realizado a un paciente con fractura extrarticular del tercio distal de la tibia, mediante una técnica de osteosíntesis percutánea mínimamente invasiva. Presentación del caso: Paciente de 45 años, masculino, de piel blanca que sufrió accidente del tránsito, y fue atendido en el servicio de Ortopedia y Traumatología del Hospital General Docente Dr. Antonio Luaces Iraola, con trauma en pierna izquierda. Presentó dolor, inflamación e imposibilidad para caminar. A la exploración física se constató dolor, deformidad, crepitación, movilidad anormal, aumento de volumen e impotencia funcional absoluta. Se realizó radiografía, se corroboró diagnóstico y se decidió tratamiento quirúrgico con técnica mínima invasiva percutánea. Se siguieron los principios de la osteosíntesis biológica y se utilizó placa de segunda generación del sistema AO. Conclusiones: El tiempo quirúrgico fue de 45 minutos, la estadía hospitalaria fue de 48 horas. Se comenzó apoyo parcial a las ocho semanas, y total a las 15 semanas. Se logró la consolidación total de la fractura a las 16 semanas de operado, evaluado de excelente a través de la American Orthopaedic Foot and Ankle Society (AOFAS) score(AU)

Introduction: Diaphyseal fractures of the tibia have high incidence per year, including those of the distal third. They are the most common of the long bones and are seen mostly in young adults. They are generally caused by high-energy trauma such as traffic accidents and falls from heights. Objective: To present the results of the treatment on a patient with extra-articular fracture of the distal third of the tibia, using minimally invasive percutaneous osteosynthesis technique. Case report: A white 45-year-old male patient was injured in a traffic accident, and he was treated in the Orthopedics and Traumatology service at Dr. Antonio Luaces Iraola General Teaching Hospital, because of a trauma to his left leg. He had pain, swelling and inability to walk. Physical examination revealed pain, deformity, crepitus, abnormal mobility, increased volume, and absolute functional impotence. X-rays were performed. The diagnosis was confirmed, and surgical treatment was decided with a minimally invasive percutaneous technique. The principles of biological osteosynthesis were followed and a second generation plate of AO system was used. Conclusions: The surgical time was 45 minutes. The hospital stay was 48 hours. Partial support of the leg was started at eight weeks, and full support at 15 weeks. Full fracture healing was achieved 16 weeks after surgery, the procedure was evaluated as excellent according to the American Orthopedic Foot and Ankle Society (AOFAS) score(AU)

Resultados del tratamiento quirúrgico de pacientes con cáncer pulmonar / Results of surgical treatment of patients with lung cancer

RESUMEN Fundamento: la incidencia de cáncer de pulmón en la provincia Sancti Spíritus es alta y su diagnóstico por lo general, se realiza en etapas avanzadas por lo cual el tratamiento quirúrgico no siempre es posible. Objetivo: analizar las principales características y resultados de los pacientes operados por cáncer de pulmón. Métodos: se realizó un estudio observacional descriptivo de corte transversal en el servicio de Cirugía General del Hospital Universitario General Camilo Cienfuegos en la provincia Sancti Spiritus en el período comprendido entre enero de 1996 y diciembre de 2019. El universo consistió en 83 pacientes operados con cáncer de pulmón que se sometieron a resección acompañados de muestreo de ganglios linfáticos mediastinales. Resultados: el sexo masculino predominó en el grupo estudiado. Los grupos de edades más frecuentes para ambos sexos fueron los de 51 a 60 años y los mayores de 60 años. El hábito de fumar estuvo presente en la mayoría de los pacientes. La localización tumoral más predominó fue en los lóbulos superiores y la lobectomía fue la técnica más realizada. Las etapas patológicas que predominaron fueron la lB y llB, seguidas de la lllA. El carcinoma de células escamosas fue el tipo histológico más frecuente. Las atelectasias y las infecciones respiratorias fueron las complicaciones más frecuentes. Los fallecidos fueron pocos. Conclusiones: las características demográficas de los pacientes estudiados se corresponden a otras series de pacientes con cáncer del pulmón. La localización tumoral en los lóbulos superiores, el carcinoma epidermoide, así como las etapas tempranas, predominaron en la serie estudiada. La lobectomía fue la técnica quirúrgica que se utilizó con mayor frecuencia y dentro de las complicaciones, las respiratorias fueron las más frecuentes.

ABSTRACT Background: the incidence of lung cancer in the province of Sancti Spíritus is high and its diagnosis is usually made in advanced stages, for which surgical treatment is not always possible. Objective: to analyze the main characteristics and results of patients operated on for lung cancer. Methods: a cross-sectional descriptive observational study was carried out in the General Surgery service of the Camilo Cienfuegos General University Hospital in the Sancti Spiritus province in the period between January 1996 and December 2019. The universe consisted of 83 patients operated with lung cancer who underwent resection accompanied by mediastinal lymph node sampling. Results: the male sex predominated in the studied group. The most frequent age groups for both sexes were those from 51 to 60 years old and those over 60 years old. Smoking was present in most of the patients. The most frequent tumor location was in the upper lobes and lobectomy was the most performed technique. The pathological stages that predominated were lB and llB, followed by lllA. Squamous cell carcinoma was the most frequent histological type. Atelectasis and respiratory infections were the most frequent complications. The deceased were few. Conclusions: the demographic characteristics of the patients studied correspond to other series of patients with lung cancer. Tumor location in the upper lobes, squamous cell carcinoma, as well as early stages, predominated in the series studied. Lobectomy was the most frequently used surgical technique and among complications, respiratory ones were the most frequent.

Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray photoelectron spectroscopy instruments using low-density polyethylene.

We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (<90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration.