Office dermatologic testing: the KOH preparation - potassium hydroxide
Superficial fungal infection occurs when dermatophytes, yeast or other fungi invade the outermost layer of skin, known as the stratum comeum epidermidis. When this type of infection is suspected, a potassium hydroxide (KOH) examination should be performed on a sample of skin scraping. This simple, inexpensive office test can confirm the diagnosis, permitting prompt, definitive treatment, or it can provide evidence leading to the consideration of other diagnoses.
Types of Infection:
Superficial fungal infections are usually caused by dermatophyte species and are classified by their location on the body. Tinea faciei usually presents as an enlarging, scaly, annular patch on the face. Tinea corporis appears as a similar patch or patches on the trunk or extremities. Tinea capitis may present as scaly patches of alopecia or as inflammatory boggy nodules or pustules on the scalp. Tinea cruris, sometimes referred to as "jock itch," may involve one or both medial thighs and may extend to the buttocks and posterior thighs or into the suprapubic area. Tinea pedis may give the appearance of dry skin on the soles, maceration between the toes, or vesicles or bullae on the soles or toes. Onychomycosis is fungal infection of the nails.
The lesions of eczema or psoriasis may appear quite similar to the scaly patches of a superficial fungal infection. Parapsoriasis, pityriasis rosea, lichen planus and eczematous drug eruptions can also be mistaken for fungal infections.
Superficial fungal infections may be caused by yeast organisms such as Candida albicans or Malassezia furfur. C. albicans can cause thrush (oral candidiasis), angular cheilitis, perliche (candidal infection at the corners of the mouth), intertrigo (infection between opposed surfaces of the skin), balanitis and vaginitis. M. furfur is responsible for tinea versicolor. This infection is usually manifested by fawn-colored or hypopigmented scaly patches on the trunk and the proximal extremities. The hypopigmented patches resemble pityriasis alba and may occasionally be mistaken for vitiligo.
Materials:
The materials needed for a KOH preparation include
• a 10 to 20 percent KOH solution
• Parker black or blue-black Super Quink ink
• a no. 15 scalpel blade
• a microscope slide and coverslip
• a methanol burner and a microscope Figure 1). Sampling
When obtaining a sample from the patient, it is important to collect material that is most likely to give a positive result. If the scraping is from a ringworm lesion (a dermatophyte infection), the sample should be collected from the outer rim of the lesion. Scrapings from the center of the lesion more of ten give a false-negative result. When obtaining a specimen from an apparent lesion of tinea versicolor, the scraping should be taken from the scaling patches or scaly margins of larger patches that are characteristic of this infection. If a superficial candidal infection is likely, the moist, macerated, cheesy material on the skin or mucosal surface provides the best sample.
When obtaining nail samples, it is best to look for white areas, since these are the most likely sites of active infection. I If no white areas can be detected, sampling of the subungual debris at the free end of the nail is preferred.
With candidal infection of the skin around the nails (paronychia), pus that contains yeast forms may be obtained by compressing the swollen, erythematous paronychial tissue or by incising the area with a no.II scalpel blade. This material should be placed on a microscope slide and covered with a coverslip.
If tinea capitis is suspected, a sample of the base of the patient's hair and/or scales from the affected scalp should be obtained. Wood's lamp examination is of little value since Trichophyton tonsurans, the organism that most commonly causes tinea capitis in children, does not produce fluorescence. (2) Scalp infections caused by T. tonsurans are also called black-dot ringworm. The short hairs that give the blackdot appearance should be sampled and examined for endothrix spores. Because of inflammation surrounding the hair follicle, the hair can usually be scraped with a scalpel blade or easily removed with forceps or tweezers. The scrapings and/or hair should be placed on a microscope slide and protected with a coverslip.(3)
Two important points should be kept in mind when collecting samples for KOH preparation. First, a large amount of scale should be collected to ensure a thorough examination and increase the chance of demonstrating the organism if it is present.(4) Second, a coverslip should be placed on the microscope slide immediately after collection so that the specimen does not blow away as the slide is carried from the examining room. Technique
After an appropriate area has been chosen, a no. 15 scalpel blade is used to scrape scales from the lesion onto a microscope slide. The slide is held perpendicular to the skin below the area being scraped.(5) When scraping the scales for a sample, the scalpel blade should be held with its sharp edge trailing behind so that the skin is not lacerated Figure 2). When an adequate amount of material has been obtained, a coverslip is immediately placed on the slide.
Surface passivation of cadmium zinc telluride radiation detectors by potassium hydroxide solution
The spectral resolution of cadmium zinc telluride (CZT) room temperature nuclear radiation detectors is often limited by the presence of conducting surface species that increase the surface leakage current. Surface passivation plays an important role in reducing this surface leakage current and thereby decreasing the noise ofthe detectors and improving the spectral energy resolution. Chemical etching with a Br-MeOH solution leaves CZT surfaces rich in Te and is considered as one of the primary causes of the increased surface leakage current. Previous studies have shown that hydrogen peroxide (H202) forms oxides of tellurium on the CZT surface and thus acts as a good passivating agent. In this study we will present results on the use of potassium hydroxide (KOH) as an alternative passivating agent. The KOH aqueous solution leaves a more stoichiometric (evaluated from the trends in the surface Cd:Te ratio) and smoother CZT surface. The passivation effects of KOH solution on the surface of the CZT have been characterized by current-voltage measurements for different KOH concentrations and etching times for both parallel strip electrodes as well as a metal-semiconductor-metal configuration. The surface chemical composition and its morphology were studied by scanning x-ray photoelectron spectroscopy and atomic force microscopy. The comparison and demonstration of improvements in the spectral resolution of the CZT detectors (based on 241Am spectra) with and without the KOH treatment are presented.Key words: Gamma-ray detector, surface passivation, etching, CZT, KOH, radiation sensor, surface treatment
INTRODUCTION
The surface preparation quality of bulk CZT crystals is critical to the fabrication and performance of xand gamma-ray detectors, and thus it is useful to understand the effects of these processing variables on the crystals and on the detectors fabricated from them. The spectral resolution of CZT room temperature nuclear radiation detectors is often limited by the presence of conducting surface species that increase the surface leakage current. Surface passivation plays an important role in reducing this leakage current and attendant noise, thereby improving the spectral energy resolution particularly for low energy x-rays.
There has been a considerable amount of work done by others to increase the charge collection efficiency of room temperature CZT detectors." Several reports have also addressed the need for passivation of CZT and CdTe surfaces to reduce the surface leakage current. An increase in interstrip resistance by up to three orders of magnitude was measured following surface passivation.5 CZT surface passivation has been achieved by an oxidation treatment in a H2 aqueous solution or by an atomic oxygen bombardment.7 It has been observed that bromine methanol etch leaves the CZT surface depleted in cadmium and rich in tellurium. This residual Te film is highly conductive compared to high-resistivity bulk CZT and thus increases the surface leakage current. Most of the surface passivation treatments convert the electrically conductive tellurium film into a higher resistive layer of CdTeO3, which was proposed" earlier as the probable stable phase formed during the oxidation of CZT surfaces. In our present study we have tried to convert the Te-rich CZT surface to a more stoichiometric surface by using different chemical etchants.
EXPERIMENT :
The 5 x 5 x 2 mm3 CZT samples were obtained from eV-Products, Inc. These samples were first mechanically polished with a 0.05 gm particle size alumina suspension and then rinsed in methanol. In order to remove the mechanically damaged layer, each sample was etched for 2 min with a 5% solution of bromine in methanol (Br-MeOH), which is a standard etchant commonly used for CZT detectors, and then again rinsed in methanol. The samples were then treated with different concentrations (5%, 10%, 15%, and 20%) of KOH aqueous solution and also for different lengths of time (20 min, 40 min, 60 min, and 120 min). For the IN measurements and gamma-ray spectra, Au contacts were deposited by sputtering immediately after the chemical treatment in order to minimize the effects of surface oxidation. After the metal deposition, Pd leads were attached to the contacts using a colloidal graphite suspension in water ("aquadag" from Acheson Inc.). Finally, the device was covered with a protective coating ("Humiseal" from Chase Corp.) to isolate the surface from the ambient and also to improve the mechanical stability. The experimental set up for the IN and room temperature radiation spectral measurements have been reported earlier.9 X-ray photoelectron spectroscopy (XPS) was carried out on freshly etched samples, placed in a chamber that was evacuated to an ultrahigh vacuum of 3 x 10-10 torr. The XPS spectra were obtained with a PHI 5600 ci spectrometer equipped with a Mg KCC anode having a characteristic energy of 1253.6 eV. Spectra were also taken after treatment with in situ argon cleaning, and they were used to interpret the effectiveness of different chemical treatments. For each sample a wide XPS scan was performed to determine the relative composition and chemical species on the surface, The primary peaks of interest (Te 3d, Cd 3d) were scanned individually to optimize their spectral intensity and resolution. The spectral shift was corrected using the measured C 1 s peak and the theoretical binding energy of 284.6 eV. The surface morphology was studied by taking AFM images in the tapping mode, employing a Digital Instruments Nanoscope III multimode scanning probe microscope. It consisted of a piezoelectric scanner |
