InGaN/GaN nanowires as a new platform for photoelectrochemical sensors - detection of NADH.

InGaN/GaN nanowire heterostructures are presented as nanophotonic probes for the light-triggered photoelectrochemical detection of NADH. We demonstrate that photogenerated electron-hole pairs give rise to a stable anodic photocurrent whose potential- and pH-dependences exhibit broad applicability. In addition, the simultaneous measurement of the photoluminescence provides an additional tool for the analysis and evaluation of light-triggered reaction processes at the nanostructured interface. InGaN/GaN nanowire ensembles can be excited over a wide wavelength range, which avoids interferences of the photoelectrochemical response by absorption properties of the compounds to be analyzed by adjusting the excitation wavelength. The photocurrent of the nanostructures shows an NADH-dependent magnitude. The anodic current increases with rising analyte concentration in a range from 5µM to 10mM, at a comparatively low potential of 0mV vs. Ag/AgCl. Here, the InGaN/GaN nanowires reach high sensitivities of up to 91µAmM-1cm-2 (in the linear range) and provide a good reusability for repetitive NADH detection. These results demonstrate the potential of InGaN/GaN nanowire heterostructures for the defined conversion of this analyte paving the way for the realization of light-switchable sensors for the analyte or biosensors by combination with NADH producing enzymes.

Integration of an opto-chemical detector based on group III-nitride nanowire heterostructures.

The photoluminescence intensity of group III nitrides, nanowires, and heterostructures (NWHs) strongly depends on the environmental H(2) and O(2) concentration. We used this opto-chemical transducer principle for the realization of a gas detector. To make this technology prospectively available to commercial gas-monitoring applications, a large-scale laboratory setup was miniaturized. To this end the gas-sensitive NWHs were integrated with electro-optical components for optical addressing and read out within a compact and robust sensor system. This paper covers the entire realization process of the device from its conceptual draft and optical design to its fabrication and assembly. The applied approaches are verified with intermediate results of profilometric characterizations and optical performance measurements of subsystems. Finally the gas-sensing capabilities of the integrated detector are experimentally proven and optimized.

Electrical transport properties of Ge-doped GaN nanowires.

The conductivity and charge carrier concentration of single GaN nanowires (NWs) doped with different concentrations of Ge were determined by four-point resistivity and temperature-dependent Seebeck coefficient measurements. We observed high carrier concentrations ranging from 9.1 × 10(18) to 5.5 × 10(19) cm(-3), well above the Mott density of 1.6 × 10(18) cm(-3), and conductivities up to 625 S cm(-1) almost independent of the NW diameter. The weak temperature dependence of the conductivity between 2 and 10 K could be assigned to the formation of an impurity band. For the sample with the highest conductivity metallic behaviour was found, indicated by a positive temperature coefficient of the resistivity. The near band edge emission analyzed by micro-photoluminescence spectroscopy showed only a small increase of the peak width up to 70 meV and no spectral shift for carrier concentrations up to 5.5 × 10(19) cm(-3). The latter was attributed to the simultaneous influence of band filling, band gap renormalization, and strain.

Intraband absorption in self-assembled Ge-doped GaN/AlN nanowire heterostructures.

We report the observation of transverse-magnetic-polarized infrared absorption assigned to the s-p(z) intraband transition in Ge-doped GaN/AlN nanodisks (NDs) in self-assembled GaN nanowires (NWs). The s-p(z) absorption line experiences a blue shift with increasing ND Ge concentration and a red shift with increasing ND thickness. The experimental results in terms of interband and intraband spectroscopy are compared to theoretical calculations of the band diagram and electronic structure of GaN/AlN heterostructured NWs, accounting for their three-dimensional strain distribution and the presence of surface states. From the theoretical analysis, we conclude that the formation of an AlN shell during the heterostructure growth applies a uniaxial compressive strain which blue shifts the interband optical transitions but has little influence on the intraband transitions. The presence of surface states with density levels expected for m-GaN plane charge-deplete the base of the NWs but is insufficient to screen the polarization-induced internal electric field in the heterostructures. Simulations show that the free-carrier screening of the polarization-induced internal electric field in the NDs is critical to predicting the photoluminescence behavior. The intraband transitions, on the other hand, are blue-shifted due to many-body effects, namely, the exchange interaction and depolarization shift, which exceed the red shift induced by carrier screening.

Radical formation at the gallium nitride nanowire-electrolyte interface by photoactivated charge transfer.

We investigated the transfer of photogenerated charge carriers from GaN nanowires into a surrounding electrolyte by electron paramagnetic resonance (EPR) and fluorescence spectroscopy. Using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap we find that the formation of hydroxyl radicals dominates in acidic, neutral and moderately basic environments, while in an electrolyte with a pH of 13.5 the superoxide formation becomes detectable. We explain the two processes considering the redox potentials for radical formation in the electrolyte as well as the positions of the conduction and valence bands. The role of surface band bending and surface states in the semiconductor is discussed.

Metastatic malignant melanoma within meningioma with intratumoral infarct: report of an unusual case and literature review.

We report an unusual case of a patient with a sphenoid wing meningioma that after a few years of static radiological appearance presented with sudden deterioration following rapid growth of tumor with intratumoral infarct. The patient underwent surgery and malignant melanoma deposits within the meningioma were demonstrated on histopathological examination. She had a history of a malignant melanoma (MM) excised from the left forearm 10 months ago with no evidence of recurrence. Although metastasis to meningioma has been widely reported, this is only the second report where the primary tumor is MM. In addition, to the best of our knowledge, intratumoral hypodensity from metastasis is unusual. The tumor-to-tumor phenomenon is discussed and the literature is reviewed.

Cerebellopontine angle meningioma resulting in middle-ear polyp.

Extracranial spread of meningiomas to involve the middle ear is very rare. We present the case of a 43-year-old woman with a known cerebellopontine angle meningioma who subsequently presented with left-sided otalgia and a middle-ear mass extruding through the tympanic membrane due to local invasion of the meningioma. The tumour was excised surgically. A discussion of the relevant literature is also presented.

Intracranial non-Hodgkin's MALT lymphoma mimicking a large convexity meningioma.

Primary presentation of an intradural Non-Hodgkin's lymphoma is rare. Recently these B cell lymphomas of mucosa associated lymphoid tissue (MALT) have gained acceptance as an important pathological subtype and are distinguishable from other primary CNS lymphomas that exhibit aggressive behaviour. Over the past decade a number of these lesions have been reported to resemble a meningioma both intra-operatively and radiologically. The authors outline such a case of marginal zone B cell lymphoma that clinically and radiologically resembled a meningioma. This case illustrates the rare occurrence of low grade dural B cell lymphoma and the need to consider this entity in the differential diagnosis of CNS lesions, if appropriate targeted therapy is to be administered.

Entrapped spinal nerve roots in a pseudomeningocoele as a complication of previous spinal surgery.

Pseudomeningocele is a rare but well recognised complication of lumbar surgery (microdiscectomy and laminectomy). Most of the patients tolerate the presence of the cyst well, however some present with back pain and spinal claudication, presumably due to neural compression. We report a case who presented following three operations (microdiscectomy, laminectomy and excision of a pseudomeningocele) with symptoms of spinal claudication and bilateral radicular pain. The cause of her pain was evident only at operation and was due to herniation of nerve roots through the dural defect.

New proposals for training in neurosurgery.

The rapidly evolving changes in working patterns, career structure and the regulation of training of doctors have provided an ideal opportunity for proposals to improve the programme for the training of neurosurgeons. The Education and Training Committee of the Society of British Neurological Surgeons (D.G. Hardy, A. J. W. Steers, N. T. Gurusinghe, P. M. Foy, P. van Hille, R. A. Cowie, H. A. Crockard, O. Sparrow and S. Burn) has, in recent months, worked closely with the Specialist Advisory Committee (SAC) in neurosurgery, Department of Health (Modernizing Medical Careers Group, H. A. Crockard, A. Havers, T. Hobbs) and colleagues from the major neuroscience specialties to develop a new programme based on a 'Common Stem' approach. This article describes the principles of the programme. The proposals have received approval by the Council of the SBNS, the Presidents of the four Surgical Royal Colleges and the Senate of Surgery.

Neuromuscular hamartoma of the cochlear nerve: a rare occurrence in the internal auditory meatus.

The authors present a case of neuromuscular hamartoma of the cochlear nerve, an unusual occurrence in the internal auditory meatus (IAM). A review of the literature shows no previous report of neuromuscular hamartoma of the cochlear nerve. This tumour was clinically and radiologically difficult to distinguish from acoustic neuroma. It is important to consider the diagnosis of these rare small tumours pre-operatively, as it may be appropriate to manage this conservatively.

Haptic discrimination of size and texture in squirrel monkeys (Saimiri sciureus).

The present study analyzed haptic abilities of four squirrel monkeys. Using a two-alternative forced-choice procedure, stimuli were presented in a visually opaque box, allowing unrestrained test subjects to grab through a small opening and touch the discriminanda. Difference thresholds were determined by a modified method of limits. In the first experiment we determined size difference thresholds for the discrimination of circular cylinders using standard stimuli differing in diameter from 10 mm to 35 mm. In the second experiment a texture difference threshold was obtained for the discrimination of grooved surfaces (groove width 2-7 mm). The squirrel monkeys achieved a mean size difference threshold of 8% stimulus difference. The linear increase of absolute thresholds as a function of the starting stimulus size showed that haptic size discriminations in squirrel monkeys correspond to Weber's law. Three of the animals achieved a texture difference of 10% stimulus difference, while one monkey showed a distinctively lower haptic acuity. An analysis of the exploratory behavior points to a subject-related difference in the significance of cutaneous and kinesthetic information during size discriminations. Whereas differences in the animals' exploratory behavior did not correlate with the size difference threshold a subject achieved, different thresholds for texture discrimination can be explained by the different exploratory procedures the monkeys used to touch grooved surfaces. The low difference thresholds determined for the squirrel monkeys in the present study point to the significance of unrestrained test conditions for the assessment of the haptic capacity of a species.

Management of spontaneous cerebellar hematomas: a prospective treatment protocol.

OBJECTIVE: To identify easily applicable guidelines for the surgical and conservative management of spontaneous cerebellar hematomas. METHODS: A treatment protocol was developed and prospectively applied for the management of 50 consecutive cases of cerebellar hematomas. The appearance of the fourth ventricle, adjacent to the hematoma, on computed tomographic scans was divided into three grades (normal, compressed, or completely effaced). The degree of fourth ventricular compression was correlated with the size and volume of the hematoma and the presenting Glasgow Coma Scale (GCS) score. The hematoma was surgically evacuated for all patients with Grade III compression and for patients with Grade II compression when the GCS score deteriorated in the absence of untreated hydrocephalus. Patients with Grade I or II compression were initially treated with only ventricular drainage in the presence of hydrocephalus and clinical deterioration. RESULTS: The degree of fourth ventricular compression was classified as Grade I in 6 cases, Grade II in 26, and Grade III in 18. The degree of fourth ventricular compression was significantly correlated with the volume of the hematoma (r(s) = 0.67, P < 0.0001), hydrocephalus (r(s) = 0.44, P = 0.001), the preoperative GCS score (r(s) = 0.43, P = 0.001), the maximal diameter of the hematoma (r(s) = 0.43, P = 0.001), and a midline location of the hematoma (chi(2) = 6.84, P < 0.009). Acute deterioration in GCS scores occurred for 6 (43%) of 14 patients with Grade III ventricular compression who were conscious at presentation. Thirteen patients with Grade I or II ventricular compression and stable GCS scores of more than 13 were treated conservatively. Nine patients were treated with ventricular drainage only, and 28 underwent posterior fossa craniectomy and evacuation of the hematoma with ventricular drainage. The mortality rate at 3 months was 40%. None of the patients with Grade III fourth ventricular compression and GCS scores of less than 8 at the time of treatment experienced good outcomes. Overall, 15 (60%) of 25 patients with hematomas with maximal diameters of more than 3 cm and Grade I or II compression did not require clot evacuation. CONCLUSION: Conscious patients with Grade III fourth ventricular compression should undergo urgent clot evacuation before deterioration. Surgical evacuation of the clot may not be required for large hematomas (>3 cm) if the fourth ventricle is not totally obliterated at the level of the clot.

Hypoglossal-facial nerve anastomosis: assessment of clinical results and patient benefit for facial nerve palsy following acoustic neuroma excision.

Despite advances in neuro-otological techniques permanent complete facial palsy may still occur in up to 10% of patients undergoing removal of cerebellopontine angle tumours. Hypoglossal-facial nerve anastomosis is the procedure of choice in our unit for facial reanimation in such patients and below we report the results of hypoglossal-facial nerve anastomosis performed on 29 patients. Assessment of patient benefit from hypoglossal-facial nerve anastomosis was obtained using a questionnaire based on the Glasgow Benefit Inventory. The results showed all patients to have an improvement in their House Brackmann grade following hypoglossal-facial anastomosis with 65% achieving grade III or better. Of the 20 patients who completed the questionnaire, 18 showed a positive benefit (median score 59.5, range 40-77). There was a significant correlation (P < 0.045) between the Glasgow benefit inventory score and House Brackmann grade. Outcome was not affected by the time interval between the acoustic neuroma surgery and performing the hypoglossal-facial nerve anastomosis, sex or length of follow-up. However the Glasgow benefit score was significantly influenced by age (P = 0.023) with younger patients showing more benefit independent of improvement in facial nerve function.

Muslin induced granuloma following wrapping of intracranial aneurysms: the role of infection as an additional precipitating factor. Report of two cases and review of the literature.

Two patients who developed what appeared to be a granulomatous reaction following muslin wrapping of unclipped aneurysms are reported. They presented with cranial nerve palsies and at operation were found to have an abscess around the wrapped aneurysms. In one of these two patients Staphylococcus epidemidis was isolated from the pus. This, together with further evidence from reported cases in the literature, would suggest that infection may play an additional role at least in some cases in the onset of a foreign-body granulomatous reaction seen following wrapping of aneurysms.

Evaluation of surgery for the tethered cord syndrome using a new grading system.

A new grading system is presented to assess the degree of untethering achieved at surgery for the 'tethered cord syndrome' based on intraoperative observation at the end of the procedure. Various pathophysiological mechanisms responsible for the 'tethered cord syndrome', as well as possible factors causing retethering were considered in developing this grading system. In Grade I the cord is considered to be fully untethered and the factors potentially responsible for retethering are eliminated, in Grade II partial untethering is performed and in Grade III untethering is unsuccessful. This grading system was used to assess the results of 22 consecutive operations performed to release a tethered cord between June 1991 and February 1995. The tethering factors encountered at surgery were: spinal lipoma in 14, diastematomyelia in five, a tight filum terminale in 10 and intradural adhesions in three instances. The grade of untethering was correlated with the type of pathology encountered, postoperative results, and whether previous surgery was performed or not. Previous surgery was found not to affect the rate of subsequent successful untethering.

Cerebellar mutism following posterior fossa tumour surgery.

Two cases of transient mutism following operative removal of cerebellar medulloblastoma are reported. These add to the few cases reported in the literature of this rare complication of posterior fossa tumour surgery in children.

Radiolyo-chemiluminescence of bones and seafood shells - a new, promising method for the detection of food irradiation?

Biomineral substances are dissolved in an alkaline mixture of luminol solution and EDTA. Light emission is observed upon dissolution of irradiated calcium carbonate in mollusk and crustacean shells and calcium hydroxyapatite in bones, showing a significantly increased chemiluminescence compared to unirradiated samples. This enables the determination of exposure to ionizing radiation and in some cases even dosimetry. The method described is simple in sample preparation and fast for the detection of irradiated seafood and poultry.