Comprehensive Laboratory Evaluation of a Highly Specific Lateral Flow Assay for the Presumptive Identification of Ricin in Suspicious White Powders and Environmental Samples

Abstract

Ricin, a heterodimeric toxin that is present in the seeds of the Ricinus communis plant, is the biothreat agent most frequently encountered by law enforcement agencies in the United States. Even in untrained hands, the easily obtainable seeds can yield a highly toxic product that has been used in various types of threats, including "white-powder" letters. Although the vast majority of these threats are hoaxes, an impediment to accurate hazard assessments by first responders is the unreliability of rapid detection assays for ricin, such as lateral flow assays (LFAs). One of the complicating factors associated with LFAs is the incorporation of antibodies of poor specificity that cross-react with near-neighbors or with plant lectins that are capable of nonspecifically cross-linking the capture and detector antibodies. Because of the compelling and critical need to promote the interests of public safety and public health, the Department of Homeland Security conducted a comprehensive laboratory evaluation study of a commercial LFA for the rapid detection of ricin. This study was conducted using comprehensive inclusivity and exclusivity panels of ricin and near-neighbor plant materials, along with panels of lectins and "white-powders," to determine the specificity, sensitivity, limits of detection, dynamic range, and repeatability of the assay for the specific intended use of evaluating suspicious white powders and environmental samples in the field.

Evaluation of Immunoassays and General Biological Indicator Tests for Field Screening ofBacillus anthracisand Ricin

“…None of the immunoassay product's claimed limits of detection were achieved with our spore testing, although our ricin immunoassay results were comparable to other published studies. 19,21 As demonstrated by our preliminary studies on B. anthracis growth media and strain type, the differences between PNNL B. anthracis limit of detection estimates, manufacturer claims, and published data could be due to variations in sample preparation or spore strain type. For products that had optional optical readers, we found that the use of an optical reader does not always improve sensitivity.…”

Comprehensive Laboratory Evaluation of a Highly Specific Lateral Flow Assay for the Presumptive Identification ofBacillus anthracisSpores in Suspicious White Powders and Environmental Samples

“…48 Simple to use and requiring minimal training, 49 LFAs are ideal for use by first responders and law enforcement officers to test suspicious materials in field settings. BioThreat Alert Ò Assays have previously been evaluated for the detection of other biothreat agents, including orthopoxviruses, 50 ricin, 33 abrin, 34 and Yersinia pestis. 51 Limited evaluations have also been conducted with LFAs for the detection of Francisella tularensis (unpublished data), botulinum neurotoxins, 52 and staphylococcal enterotoxins.…”

On-site detection of bioterrorism-relevant agents

“…Während mit Labormethoden beispielsweise Toxine im ein-bis zweistelligen Picogramm-pro-Milliliter-Bereich nachgewiesen werden können [19], sind kommerzielle Lateral Flow Assays (LFA) um einen Faktor 1000 weniger empfindlich und benötigen bestenfalls wenige Nanogramm pro Milliliter für den Toxinnachweis [20]. Der Hauptgrund hierfür liegt im direkten Nachweis der Antikör-perbindung, wohingegen bei Labormethoden enzymatische Signalamplifikationsschritte zu einer deutlichen Steigerung der Sensitivität führen [21].…”