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Self-powered sensor is considered as a promising, rapid, portable and miniaturized detection device that can work without external power input. In this work, a novel dual-photoelectrode self-powered aptasensor for digoxin detection was designed on the basis of a photofuel cell (PFC) composed of a black TiO2 (B–TiO2) photoanode and a CuBr photocathode in a single-chamber cell. The sensing platform avoided the use of membrane, free mediator, bioactive components and costly metal Pt electrodes. The large inherent bias between the Fermi energy level of B–TiO2 and that of CuBr improved the electricity output of PFC that the open circuit potential (OCP) and the maximum power density (Pmax) reached 0.58 V and 6.78 μW cm-2 respectively. Based on the excellent output of PFC, digoxin aptamer was immobilized on photoanode as the recognition element to capture digoxin molecules, which realized the high sensitive and selective detection of digoxin. The self-powered aptasensor displayed a broad linear in the range from 10-12 M to 10-5 M with a detection limit (3 S/N) of 0.33 pM. This work paved a luciferous way for further rapid, portable, miniaturized and on-site self-powered sensors.

Background Oleander interferes with serum digoxin measurements using various immunoassays. The potential interference of oleander and its active ingredient, oleandrin, with a relatively new homogenous sequential chemiluminescent digoxin assay based on luminescent oxygen channeling technology (LOCI digoxin assay, Siemens Diagnostics) has not been previously reported. Methods Aliquots of a digoxin-free serum pool were supplemented with increasing concentrations of oleandrin, or with oleander extract, followed by measuring the apparent digoxin concentrations using the LOCI digoxin assay using Vista 1500 analyzer. Mice were fed oleandrin or oleander extract, and their blood digoxin levels at 1 and 2 h were measured with the LOCI digoxin assay. In addition, two digoxin serum pools were prepared by combining sera of patients receiving digoxin; aliquots of both pools were supplemented with oleandrin or oleander extract and digoxin concentrations were again measured. Attempts to overcome this interference were made by measuring free digoxin concentration using a third digoxin pool. Results Significant apparent digoxin concentrations were observed after supplementing aliquots of the drug-free serum pool with oleandrin or oleander extract. Mice fed with oleandrin or oleander extract also showed apparent digoxin levels 1 and 2 h after feeding. Digoxin values were also falsely lower or elevated (bidirectional interference) when aliquots of digoxin serum pools were further supplemented with oleandrin or oleander extract depending on concentration; this interference was not eliminated by free digoxin monitoring. Conclusions Oleandrin interferes with LOCI digoxin assay.

Objective To determine what triggers the use of digoxin therapeutic drug monitoring (TDM) that adheres to established indications and the change in digoxin dosage after the result of monitoring is obtained. Methods This prospective study included 86 patients admitted to 6 medicine wards and 2 intensive cardiac care unit wards in a tertiary-care center. Data on patients' demographics, drug therapy, serum chemistry values, indications for digoxin therapy, indications for ordering the drug assay, timing of the blood sample relative to administration of the last dose, and physicians' decisions after attaining serum digoxin concentrations were collected. Results Eighty-six digoxin assays were evaluated. Indications for the use of a digoxin assay were mostly routine without a clear indication (66%); in only 22% of the assays were orders considered clinically justified. Eleven patients had concentrations >2 ng/mL, but only 8 patients had digoxin intoxication. In only 31% of patients did the medical staff respond to the results. In only 21% of patients with subtherapeutic drug concentrations was there a change in digoxin dose. Conclusions Although there are clear indications for the use of digoxin TDM, physicians seem to routinely order these blood tests. The clinicians did not adequately use the digoxin concentration data to optimize therapy. The assistance of a clinical pharmacist or pharmacologist is warranted for use of the assays, to optimize digoxin therapy.

Therapeutic drug monitoring of digoxin is well established in the clinical management of cardiac patients treated with the drug. Recently, target concentrations have been revised in patients with congestive heart failure to 0.5 to 0.8 microg/L, challenging the sensitivity limits of most immunoassays. These widely used methods are often criticized, particularly on specificity grounds resulting from interference from exogenous and endogenous sources. One solution to remove higher molecular weight interference has been to ultrafilter plasma samples before assaying. The present study included 261 patient digoxin samples and compared two commercial ultrafiltration devices (Centrifree and Micrcon) that share the same separation membrane (YM-30). The results showed widely discordant apparent unbound digoxin concentrations in the ultrafiltrate from these devices with a Deming regression line of Centrifree = 1.31 x Micrcon + 0.042 (95% confidence interval for slope of 1.237 to 1.391) and apparent unbound fractions ranging from 15% to 610% of the unfiltered plasma digoxin concentrations, suggesting that ultrafiltration did not resolve such interference issues. The concept of measuring lower unbound digoxin concentrations as a result of lower therapeutic range for total (bound plus unbound) digoxin will also render most immunoassays insensitive and inappropriately calibrated. There is a strong imperative to review digoxin monitoring practices in the light of current clinical imperatives for both specificity and sensitivity reasons.

“Outcomes Assessment” has become one of the enduring buzzwords of the decade. But it often seems to be like the weather: Everyone talks about it, but relatively few do anything about it. As clinical laboratory scientists, we have repeatedly challenged ourselves to demonstrate that laboratory results affect patient outcome. Yet very few well-done studies have been published. (How many times have you heard and read the results of those few studies by now?) One difficulty is the universal use of laboratory testing. Would it be acceptable to deny laboratory testing to a control group? The field of point-of-care testing (POCT) offers a major opportunity, because there are many tests not yet in widespread use. This allows ethical comparisons to be designed. (Imagine presenting to the Human Investigation Committee a study of the benefit of digoxin monitoring using a control group in which no digoxin measurements were allowed. Would they approve it? Such a study was done when digoxin assays were just being introduced and convincingly demonstrated a 50% reduction in clinical digitalis toxicity in monitored patients (1).) Another barrier is the tendency to focus on medical outcomes: decreased mortality or morbidity, shorter length of stay, decreased readmission rate, improved quality of life, etc. Medical interventions may directly alter medical outcomes, but laboratory tests do not. The effect of a test result is always filtered through the change in medical management it engenders. The ability to link the test result to the outcome requires a good correlation between the result and the therapeutic intervention. The size and duration of studies needed to establish the effectiveness of medical interventions are well known. How much larger and longer must a study be to average out the additional variation in the test itself and in the linkage between result and intervention? (Despite such …

The digoxin therapeutic drug monitoring service was evaluated during a 7-week period at Leeds General Infirmary. Data were collected for 88 patients who had one or more assays performed. The requesting clinician was contacted for each assay, and a questionnaire completed. Results were assessed to determine the appropriateness of the assay request and the action taken following receipt of the result. During the assessment period, 113 serum digoxin assays were requested. Data were collected for 88 (78%) of these, of which 22 (25%) were considered to have met all the criteria for an appropriate assay request and subsequent action. A total of 66 (75%) serum digoxin assays were assessed as wasted. The digoxin therapeutic drug monitoring service is used inappropriately at Leeds General Infirmary.