Diagnostic efficacy of high-frequency Grey-scale ultrasonography and Sono-elastography in grading the severity of carpal tunnel syndrome in comparison to nerve conduction studies.

OBJECTIVES: To correlate the cross-sectional area (CSA) and elasticity of the median nerve (MN) measured at carpal tunnel inlet between healthy controls and various degrees of carpal tunnel syndrome (CTS) graded as per nerve conduction studies (NCS). MATERIALS AND METHODS: A total of 53 patients (with 81 wrists) presenting with clinical symptoms characteristic of CTS, having their diagnosis confirmed and severity graded by NCS, and 48 healthy controls (with 96 wrists) were included in the study. All the study participants underwent wrist ultrasound which included initial Grey-scale USG followed by strain and shear wave elastography. The CSA and elasticity (in terms of strain ratio and shear modulus) of MN were measured at the carpal tunnel inlet. Statistical analysis was performed using the Mann-Whitney U test to compare between the two groups and for subgroup analysis of cases. The diagnostic performance of each variable was evaluated using the receiver operating characteristic curves. RESULTS: The mean CSA was 9.20 ± 1.64, 11.48 ± 1.05, 14.83 ± 1.19 and 19.87 ± 2.68 mm2, the mean shear modulus was 17.93 ± 2.81, 23.59 ± 2.63, 32.99 ± 4.14 and 54.26 ± 9.24 kPa and the mean strain ratio was 5.26 ± 0.68, 5.56 ± 0.70, 7.03 ± 0.47 and 8.81 ± 0.94 in control, mild, moderate and severe grades of CTS, respectively (p < 0.001). CONCLUSION: The combined utility of Grey-scale USG and Elastography may serve as a painless and cost-effective alternative to NCS in grading the severity of CTS.

Understanding ASPECTS of stroke: Inter-rater reliability between emergency medicine physician and radiologist in a rural setup.

PURPOSE: The purpose is to determine the inter-rater reliability in grading ASPECTS score, between emergency medicine physician at first contact and radiologist among patients with acute ischemic stroke. MATERIALS AND METHODS: We conducted a prospective analysis of 765 acute ischemic stroke cases referred to the Department of Radiodiagnosis in a rural-based hospital in South India, during January 2017 to October 2021. Non-contrast computed tomography (NCCT) scans of the brain were performed using GE Bright Speed Elite 128 Slice CT Scanner. ASPECTS score was calculated separately by an emergency medicine physician and radiologist. Inter-rater reliability for total and dichotomized ASPECTS (≥6 and <6) scores were assessed using statistical analysis (ICC and Cohen ĸ coefficients) on SPSS software (v17.0). RESULTS: Inter-rater agreement for total and dichotomized ASPECTS was substantial (ICC 0.79 and Cohen ĸ 0.68) between the emergency physician and the radiologist. Mean difference in ASPECTS between the two readers was only 0.15 with standard deviation of 1.58. No proportionality bias was detected. The Bland-Altman plot was constructed to demonstrate the distribution of ASPECTS differences between the two readers. CONCLUSION: Substantial inter-rater agreement was noted in grading ASPECTS between emergency medicine physician at first contact and radiologist, thereby confirming its robustness even in a rural setting.

Magnetic Resonance Imaging Characterization of the Hippocampi in Temporal Lobe Epilepsy: Correlation of Volumetry and Apparent Diffusion Coefficient with Laterality and Duration of Seizures.

Background and Purpose It is estimated that hippocampal damage is seen in 50 to 70% of patients with temporal lobe epilepsy (TLE). Although most magnetic resonance imaging (MRI) studies are adequate to detect gross hippocampal atrophy, subtle changes that may characterize early disease in TLE, such as visually nonappreciable volume loss, may often be missed if objective volumetric analysis is not undertaken. Materials and Methods We conducted a hospital-based prospective analytical study in which 40 patients with partial seizures of temporal lobe origin were included and their hippocampal volumes (HVs) were determined by manual volumetric analysis. The findings were recorded and correlated with the side of seizure and its duration. The quantitative assessment was allotted different grades accordingly. Also, the apparent diffusion coefficient (ADC) values of bilateral hippocampi were estimated and their correlation with the side of seizure was determined. Results Most patients in the study were in the age group of 11 to 20 years (37.5%). In total, 57.5% had seizures for a period of 1 to 5 years. While 67.5% ( n = 27) had seizure on the right, 32.5% ( n = 13) had on the left. The mean HV estimated on the right and left were correlated with the side of seizure and found to be statistically significant ( p < 0.001 in those with right-sided seizures and p = 0.02 in those with left-sided seizures). Simultaneously the ADC values estimated were found to correlate with the laterality of seizures with a statistical difference ( p < 0.01) . Duration of seizures however did not show a positive correlation with the HV. Conclusion MRI with quantitative estimation of HV and ADC values can depict the presence and laterality in TLE with accuracy rates that exceed those achieved by visual inspection alone. Thus, quantitative MRI provides a useful means for translating volumetric analysis into clinical practice.

SPS(Kayexalate)/CPS(K-Bind) crystals in the gastrointestinal tract-An experience from a tertiary center.

INTRODUCTION: Kayexalate (Sodium Polystyrene Sulfonate/SPS) and K-bind (Calcium Polystyrene Sulfonate/CPS) are cation exchange resins, commonly used for treatment of hyperkalaemia. SPS/CPS induced injury of the gastrointestinal tract(GIT) is rare, can be potentially life threatening but is under-recognized. This study aims to increase awareness of pathologists and clinicians of this under-reported complication of a drug commonly used to treat hyperkalaemia. MATERIALS: Study population comprised patients with SPS/CPS (Kayexalate or its analogues) crystals identified in gastrointestinal specimens from 2017-2019 at a tertiary care centre. Clinical details, relevant investigations, imaging and endoscopic findings, patient follow up details were obtained from the hospital electronic information system. RESULTS: A total of 10 patients with SPS/ CPS crystals in the GIT were encountered over 2 years. Male to female ratio was 9:1, with mean age 66.5years (range 52-82 years). Eight cases were mucosal biopsies and 2 were resection specimens. Additional pathology (tumours, colonic perforation) was present in 80% of patients. The characteristic morphological appearance of the CPS/SPS crystals on H&E stains were supported by special stains -Periodic acid Schiff(PAS) and Acid fast Bacilli(AFB). In all cases, the treatment history with SPS/CPS for hyperkalaemia was obtained only after the histological examination. Most common etiology of hyperkalaemia encountered was chronic kidney disease(CKD)/ Acute on chronic kidney disease. CONCLUSION: It is important for pathologists to recognise the presence of these crystals especially in small biopsies as early feedback to clinicians can help in appropriate management and avoidance of more serious adverse outcome. To the best of our knowledge, this is the first series of 10 consecutive cases of SPS/CPS crystals encountered in gastrointestinal tract to be reported from India.

Magnetic resonance imaging evaluation of posterior spinal tuberculosis: a cross-sectional study.

BACKGROUND: Isolated posterior spinal (element) tuberculosis (TB) is uncommon compared to classical anterior spinal or para-discal TB. Here, we report magnetic resonance imaging (MRI) findings of posterior spinal TB in 19 patients without involvement of the vertebral body and intervertebral disc. PURPOSE: To evaluate the MRI findings in isolated posterior spinal (element) TB. MATERIAL AND METHODS: Clinical and MRI data of 19 patients of isolated posterior spinal TB were retrospectively evaluated. RESULTS: Of the 19 patients, group A comprised 4 (21%) patients with rapid onset lower limb weakness and pyramidal signs while group B comprised 15 (79%) patients without any neurological deficit. Lumbar vertebrae commonly affected 9 (47.4%) patients followed by dorsal vertebrae in 8 (42.1%) patients and cervical vertebrae in 2 (10.5%) patients. The pedicle was most commonly involved in 12 (63.2%) patients followed by the lamina in 11 (58%) patients, and spinous process and facet joint in 6 (31.6%) patients each. Extra-spinal inflammation/pyomyositis/paraspinal abscess was found in 13 (68.4%) patients followed by epidural abscess 3 (15.8%) patients and both extra spinal inflammation and epidural abscess in 3 (15.8%) patients (15.8%). Compressive cord myelopathy was observed in 4 (21%) patients, where three patients underwent emergency decompression laminectomy and the remaining 16 patients were treated conservatively with anti-tubercular therapy. CONCLUSION: Initial diagnosis of isolated posterior element TB is challenging and requires a high index of suspicion. Early diagnosis of isolated posterior spinal TB is important as early treatment may be beneficial and decreases patient morbidity.

Sterilization of N95 respirators: The time for action is upon us!

Re-processing of primary protective equipment is the need of the hour with healthcare systems all over the world strained due to the shortage precipitated by severe acute respiratory syndrome coronavirus 2. The common methods of re-sterilization do not hold well for filtering facepiece respirators (FFRs) as they affect their structure and function. We propose the validation and eventual use of gamma irradiation, an already existing method of re-sterilization, to disinfect FFRs in bulk.

Biliary strictures complicating living donor liver transplantation: Problems, novel insights and solutions.

Biliary stricture complicating living donor liver transplantation (LDLT) is a relatively common complication, occurring in most transplant centres across the world. Cases of biliary strictures are more common in LDLT than in deceased donor liver transplantation. Endoscopic management is the mainstay for biliary strictures complicating LDLT and includes endoscopic retrograde cholangiography, sphincterotomy and stent placement (with or without balloon dilatation). The efficacy and safety profiles as well as outcomes of endoscopic management of biliary strictures complicating LDLT is an area that needs to be viewed in isolation, owing to its unique set of problems and attending complications; as such, it merits a tailored approach, which is yet to be well established. The diagnostic criteria applied to these strictures are not uniform and are over-reliant on imaging studies showing an anastomotic narrowing. It has to be kept in mind that in the setting of LDLT, a subjective anastomotic narrowing is present in most cases due to a mismatch in ductal diameters. However, whether this narrowing results in a functionally significant narrowing is a question that needs further study. In addition, wide variation in the endotherapy protocols practised in most centres makes it difficult to interpret the results and hampers our understanding of this topic. The outcome definition for endotherapy is also heterogenous and needs to be standardised to allow for comparison of data in this regard and establish a clinical practice guideline. There have been multiple studies in this area in the last 2 years, with novel findings that have provided solutions to some of these issues. This review endeavours to incorporate these new findings into the wider understanding of endotherapy for biliary strictures complicating LDLT, with specific emphasis on diagnosis of strictures in the LDLT setting, endotherapy protocols and outcome definitions. An attempt is made to present the best management options currently available as well as directions for future research in the area.

Endoscopic Ultrasound-Guided Rendezvous Procedure for a Nondilated, Leaking Pancreatic Duct.

Pancreatic duct (PD) leak leading to pancreatic ascites is a serious complication of chronic pancreatitis. Endoscopic management with endoscopic retrograde cholangiopancreatography (ERCP) has been found to be successful; however, if selective cannulation of the PD is unsuccessful, an endoscopic ultrasound-guided rendezvous procedure can help in bridging PD leaks, provided the duct is dilated. We report a successful endoscopic ultrasound-guided rendezvous procedure in a patient with PD leak, pancreatic ascites, and a nondilated duct with failed ERCP who was a poor candidate for surgery. The pancreatic ascites resolved following the procedure.

Bimelic symmetric Hirayama disease: Spectrum of magnetic resonance imaging findings and comparative evaluation with classical monomelic amyotrophy and other motor neuron disease.

Background: The aim of the study was to evaluate the magnetic resonance imaging (MRI) findings in bilateral symmetrical Hirayama disease and find out MRI features which are probably more indicative of symmetrical Hirayama disease, thereby help in differentiating this entity from other motor neuron disease (MND). Methods: This prospective as well as retrospective study was carried out from December 2010 to September 2016 in a tertiary care center of northeast India on 92 patients with Hirayama disease. Only 19 patients having bilateral symmetric upper limb involvement at the time of presentation were included in this study sample. Results: Nineteen patients, who constituted 20.6% of 92 patients of clinical and flexion MRI confirmed Hirayama disease were found to have bilateral symmetrical wasting and weakness of distal upper limb muscles at the time of presentation. Mean ± standard deviation (SD) age of onset of the disease process was 21.7 ± 3.8 years with mean ± SD duration of illness of 3.6 ± 1.3 years. MRI revealed lower cervical cord flattening in 13 (68.4%) patients which was symmetrical in 6 (31.6%) patients and asymmetrical in 7 (36.8%) patients. In the majority of these patients, T2-weighted images (T2WI) cervical cord hyperintensities were found extending from C5 to C6 vertebral level. Seven (36.8%) patients in our study showed bilateral symmetric T2WI hyperintensities in anterior horn cells (AHC). Conclusion: Bilateral symmetrical involvement of Hirayama disease is an uncommon presentation. Symmetrical cervical cord flattening, T2WI cord and/or bilateral AHC hyperintensities were the major MRI findings detected. Flexion MRI demonstrated similar findings in both bimelic amyotrophy and classical unilateral amyotrophy. However, flexion MRI produced some distinguishing features more typical for bilateral symmetrical Hirayama disease which help to differentiate it from other MNDs.

Spectrum of MRI Appearance of Mayer-Rokitansky-Kuster-Hauser (MRKH) Syndrome in Primary Amenorrhea Patients.

INTRODUCTION: Mayer-Rokitansky-Kuster-Hauser (MRKH) synd-rome is a malformation in female genital tract due to interrupted embryonic development of para-mesonephric ducts leading to uterine and proximal vagina aplasia or hypoplasia. AIM: To analyse the MRI findings in females suspected of MRKH syndrome in a primary amenorrhea workup. MATERIALS AND METHODS: A cross-sectional study comprising of 11 patients of MRKH syndrome presented in a tertiary care centre from March 2016 to February 2017 evaluated in 1.5 Tesla MRI scanner. RESULTS: Normal positioned small vestigial uterus demonstrated in two patients (18.2%) and complete uterine and proximal vaginal agenesis were noted in nine patients (81.8%). The mean volume of rudimentary right uterine bud was 2.26 mL ±3.3 (SD) and left uterine bud was 1.27 mL±1.1 (SD). The mean volume of right ovary was 4.74 mL±2.58 (SD) and left ovary was 4.65 mL±2.2 (SD). The mean developed vaginal length was 26.2 mm±6.34 (SD). CONCLUSION: The rudimentary uterine buds associated with MRKH syndrome always maintained caudal relationship with ovary. Ovaries or rudimentary uterine buds can be ectopic and should be recognized with MRI before undergoing fertility treatment. Following MRI diagnosis, surgery allows patients to have sexual function with possible attainment of reproduction after assisted reproduction technique or surrogacy.

Extra-pituitary Cerebral Anomalies in Pediatric Patients of Ectopic Neurohypophysis: An Uncommon Association.

CONTEXT: Ectopic neurohypophysis (EN) refers to an interrupted, nonvisualized, and thinned out pituitary stalk with ectopic location of the posterior pituitary gland. Concurrent extra-pituitary cerebral and extra-cranial anomalies have been rarely reported in patients of EN. AIM: The aim of this study was to evaluate the magnetic resonance imaging (MRI) findings of extra-pituitary cerebral anomalies in pediatric patients of EN. SETTINGS AND DESIGN: A hospital-based cross-sectional study was conducted in a tertiary care center. SUBJECTS AND METHODS: The study group comprised eight pediatric patients of EN associated with extra-pituitary cerebral or vascular anomalies. Clinical and biochemical assessment was done in all patients. RESULTS: Out of the total eight patients with EN, MRI showed interrupted pituitary stalk in five patients (62.5%) and nonvisible pituitary stalk in three patients (37.5%). Ectopic posterior pituitary bright spot was demonstrated in median eminence in six patients (75%), faintly visualized in one patient (12.5%) and nonvisualized in another one patient. Statistical significant association was noted between pituitary gland height and patient's body height with the pituitary gland volume (P < 0.001). Varied extra-pituitary cerebral anomalies encountered in our patients ranged from isolated anomalies such as optic nerve hypoplasia in three patients (37.5%), corpus callosum dysplasia in four patients (50%), agyria-pachygyria complex in two patients (25%), and intracranial vascular anomalies in two patients to syndromic association of tuberous sclerosis in one patient. CONCLUSION: Identifying and reporting of associated extra-pituitary cerebral anomalies in patients with EN are crucial in assessing the overall neurological outcome of such patients.

Role of Cross Sectional Imaging in Isolated Chest Wall Tuberculosis.

INTRODUCTION: Isolated chest wall tuberculosis though a rare entity, the incidence of it has been on rise among immunocompromised population making it an important challenging diagnosis for the physicians. Its clinical presentation may resemble pyogenic chest wall abscess or chest wall soft tissue tumour. Sometimes it is difficult to detect clinically or on plain radiograph. AIM: The present study was conducted with an aim to evaluate the common sites and varying appearances of isolated chest wall tuberculosis. MATERIALS AND METHODS: A hospital based cross-sectional retrospective study was conducted in Assam Medical College and Hospital, a tertiary care centre in North East India. The study group comprise of 21 patients (n=15 male and n=6 females) with isolated chest wall tuberculosis without associated pulmonary or spinal involvement who were subjected to Computed Tomography/Magnetic Resonance Imaging (CT/MRI) of the thorax following initial Ultrasonogram (USG) evaluation of the local site. Pathological correlation was done from imaging guided sampling of the aspirate or surgery. RESULTS: Variable sites of involvement were seen in the chest wall in our patients (n=21), with chest wall abscess formation being the most common presentation and rib being the most common bony site affected in the thoracic cage. Bony sclerosis was noted in 11 patients (52.4%), periosteal reaction in 10 patients (47.6%) and sequestration in five patients (23.8%). CT/MRI not only localized the exact site and extent of the abscesses which facilitated guided aspirations, but also helped in detecting typical bony lesions thereby, differentiating from pyogenic osteomyelitis besides ruling out associated pulmonary or pleural involvement in such patients. CONCLUSION: Cross-sectional imaging plays an important role by giving a wholesome picture of both soft tissue and bony pathology. It is important to have adequate understanding of the radiologic manifestations of the chest wall involvement and complications of tuberculosis to facilitate diagnosis and in assessing response to treatment on follow up in patients.

Magnetic Resonance Imaging Analysis of Caudal Regression Syndrome and Concomitant Anomalies in Pediatric Patients.

OBJECTIVE: The aim of this study was to evaluate the magnetic resonance imaging (MRI) findings of caudal regression syndrome (CRS) and concomitant anomalies in pediatric patients. MATERIALS AND METHODS: A hospital-based cross-sectional retrospective study was conducted. The study group comprised 21 pediatric patients presenting to the Departments of Radiodiagnosis and Pediatric Surgery in a tertiary care hospital from May 2011 to April 2016. All patients were initially evaluated clinically followed by MRI. RESULTS: In our study, 21 pediatric patients were diagnosed with sacral agenesis/dysgenesis related to CRS. According to the Pang's classification, 2 (9.5%) patients were Type I, 5 (23.8%) patients were Type III, 7 (33.3%) patients were Type IV, and 7 (33.3%) patients were of Type V CRS. Clinically, 17 (81%) patients presented with urinary incontinence, 6 (28.6%) with fecal incontinence, 9 patients (42.9%) had poor gluteal musculatures and shallow intergluteal cleft, 7 (33.3%) patients had associated subcutaneous mass over spine, and 6 (28.6%) patients presented with distal leg muscle atrophy. MRI showed wedge-shaped conus termination in 5 (23.8%) patients and bulbous conus termination in 3 (14.3%) patients above the L1 vertebral level falling into Group 1 CRS while 7 (33.3%) patients had tethered cord and 6 (28.6%) patients had stretched conus falling into Group 2 CRS. CONCLUSION: MRI is the ideal modality for detailed evaluation of the status of the vertebra, spinal cord, intra- and extra-dural lesions and helps in early diagnosis, detailed preoperative MRI evaluation and assessing concomitant anomalies and guiding further management with early institution of treatment to maximize recovery.

The safe zone for blinded sternal interventions based on CT evaluation of midline congenital sternal foramina.

OBJECTIVE: The aim of this study was to evaluate the safe zone for performing blind sternal procedures based on computed tomography (CT) evaluation of congenital midline sternal foramina using multidetector computed tomography (MDCT). MATERIALS AND METHODS: This retrospective study was carried out on 1,180 patients who underwent MDCT of the thorax from March 2015 to February 2016. The MDCT images were evaluated in axial and reformatted planes. Morphometry and prevalence of midline congenital sternal foramina (SF) and manubrio-foraminal distance (MFD) were evaluated. The safe zone was defined for a blinded intervention, based on palpable anatomical landmarks. Data were presented in terms of percentage, mean ± standard deviation and calculations were carried out using Microsoft Excel. RESULTS: The prevalence of SF in our study sample was 11.6 %. The majority of SF were located in a typical position in the lower sternal body at the level of fifth costo-chondral junction (CCJ) in 108 patients (78.8 %). The structure directly beneath the SF was mediastinal fat in 73 patients (53.3 %), followed by anterior pericardium in 44 patients (32.1 %) and lung parenchyma in 20 patients (14.6 %). The mean MFD in our study population was 11.90 ± 1.31 cm. CONCLUSIONS: Sternal interventions should be avoided at the level of fourth to sixth CCJ, which is considered the danger zone. An intervention at the fourth to sixth CCJ may lead to disastrous consequences in patients who have SF.

Acute pulmonary melioidosis in a child: A case report and review of literature.

Melioidosis is a rare potentially fatal infection caused by the bacterium Burkholderia pseudomallei, which is endemic in Southeast Asia and Northern Australia and an emerging pathogen in India. It is a largely under-diagnosed disease and an imitator of tuberculosis, both clinically and radiologically.

A multiplexed separation of iron oxide nanocrystals using variable magnetic fields.

The size-dependent magnetic properties of nanocrystals are exploited in a separation process that distinguishes particles based on their diameter. By varying the magnetic field strength, four populations of magnetic materials were isolated from a mixture. This separation is most effective for nanocrystals with diameters between 4 and 16 nm.

Low temperature synthesis of ZnS and CdZnS shells on CdSe quantum dots.

Methods for synthesizing quantum dots generally rely on very high temperatures to both nucleate and grow core and core-shell semiconductor nanocrystals. In this work, we generate highly monodisperse ZnS and CdZnS shells on CdSe semiconductor nanocrystals at temperatures as low as 65 degrees C by enhancing the precursor solubility. Relatively small amounts of trioctylphosphine and trioctylphosphine oxide have marked effects on the solubility of the metal salts used to form shells; their inclusion in the precursor solutions, which use thiourea as a sulfur source, can lead to homogeneous and fully dissolved solutions. Upon addition to suspensions of quantum dot cores, these precursors deposit as uniform shells; the lowest temperature for shell growth (65 degrees C) yields the thinnest shells (d < 1 nm) while the same process at higher temperatures (180 degrees C) forms thicker shells (d approximately 1-2 nm). The growth of the shell structures, average particle size, size distribution, and shape were examined using optical spectroscopy, transmission electron microscopy, x-ray diffraction, and transmittance small angle x-ray scattering. The photoluminescence quantum yield (QY) of the as-prepared CdSe/ZnS quantum dots ranged from 26% to 46% as compared to 10% for the CdSe cores. This method was further generalized to CdZnS shells by mixing cadmium and zinc acetate precursors. The CdSe/CdZnS nanocrystals have a thicker shell and higher QY (40% versus 36%) as compared to the CdSe/ZnS prepared under similar conditions. These low temperature methods for shell growth are readily amenable to scale-up and can provide a route for economical and less energy intensive production of quantum dots.

Pollution magnet: nano-magnetite for arsenic removal from drinking water.

Arsenic contamination in groundwater is a severe global problem, most notably in Southeast Asia where millions suffer from acute and chronic arsenic poisoning. Removing arsenic from groundwater in impoverished rural or urban areas without electricity and with no manufacturing infrastructure remains a significant challenge. Magnetite nanocrystals have proven to be useful in arsenic remediation and could feasibly be synthesized by a thermal decomposition method that employs refluxing of FeOOH and oleic acid in 1-octadecene in a laboratory setup. To reduce the initial cost of production, $US 2600/kg, and make this nanomaterial widely available, we suggest that inexpensive and accessible "everyday" chemicals be used. Here we show that it is possible to create functional and high-quality nanocrystals using methods appropriate for manufacturing in diverse and minimal infrastructure, even those without electricity. We suggest that the transfer of this knowledge is best achieved using an open source concept.

Bilayers as phase transfer agents for nanocrystals prepared in nonpolar solvents.

The effective water dispersion of highly uniform nanoparticles synthesized in organic solvents is a major issue for their broad applications. In an effort to overcome this problem, iron oxide and cadmium selenide nanocrystals were surrounded by lipid bilayers to create stable, aqueous dispersions. The core inorganic particles were originally generated in oleic acid and 1-octadecene. When these organic solutions were mixed with water and a sparing amount of excess fatty acid, up to 70% of the nanoparticles transferred into the aqueous phase. This simple approach was applied to two different nanocrystal types, and nanocrystal diameters ranging from 5 to 15 nm. In all cases, the resulting materials were stable, nonaggregated suspensions that retained their original magnetic and optical properties. The phase transfer efficiency is maximum when very little oleic acid is added (e.g. 0.2 w/w %). At higher concentrations, above the critical micelle concentration, the formation of micelles begins to compete with bilayer generation leading to less effective phase transfer. Unlike other approaches for water dispersion that rely on amphiphiles with significant water solubility, the fatty acids used in this work are only sparingly soluble in water. As a result, there is minimal dynamic exchange between free and bound surface agents and the resulting aqueous solutions contain little residual free organic carbon. Thermogravimetric analysis (TGA) confirmed the presence of bilayers around the nanocrystal cores. The particle size, size distribution, process yield, and colloidal stability were found using a suite of methods including transmission electron microscopy, small angle X-ray scattering, dynamic light scattering, inductively coupled plasma-optical emission spectroscopy, and ultraviolet-visible spectroscopy. Bilayer-nanocrystal complexes possess many of the same size-dependent features as the original materials, and as such offer new avenues for exploring and exploiting the interface between nanocrystals and biology.

Low-field magnetic separation of monodisperse Fe3O4 nanocrystals.

Magnetic separations at very low magnetic field gradients (<100 tesla per meter) can now be applied to diverse problems, such as point-of-use water purification and the simultaneous separation of complex mixtures. High-surface area and monodisperse magnetite (Fe3O4) nanocrystals (NCs) were shown to respond to low fields in a size-dependent fashion. The particles apparently do not act independently in the separation but rather reversibly aggregate through the resulting high-field gradients present at their surfaces. Using the high specific surface area of Fe3O4 NCs that were 12 nanometers in diameter, we reduced the mass of waste associated with arsenic removal from water by orders of magnitude. Additionally, the size dependence of magnetic separation permitted mixtures of 4- and 12-nanometer-sized Fe3O4 NCs to be separated by the application of different magnetic fields.