Plasmonic chip tackles type 1 diabetes diagnosis.

Diabetes mellitus is a group of metabolic disorders of carbohydrate metabolism in which patients develop hyperglycemia. Type 1 diabetes results from cellularmediated autoimmune destruction of the insulinproducing pancreatic -cells (1 ). Patients with type 1 diabetes frequently present with acute symptoms, including life-threatening ketoacidosis, and all patients require lifelong insulin therapy. Type 2 diabetes, which accounts for approximately 90% of all diabetes, has an insidious onset due to combined insulin resistance and insufficient insulin production. In many patients, type 2 diabetes can be controlled with diet, exercise, and oral agents. The worldwide incidence of diabetes has been increasing dramatically. Although most of the rise has been for type 2 diabetes, type 1 has climbed by 2.8% to 4.0% per annum, rising 21% in US youth between 2001 and 2009. At disease onset, most type 1 diabetes patients have autoantibodies to 1 or more of the following: islet cell cytoplasm, insulin [insulin autoantibodies (IAAs)], the 65-kDa isoform of glutamic acid decarboxylase (GAD65), insulinoma-associated antigen 2 (IA-2), and zinc transporter 8 (ZnT8) (these are collectively termed islet autoantibodies). Moreover, the presence of islet autoantibodies predicts the development of type 1 diabetes. A recent prospective study measured IAA, GAD65, and IA-2 in 13377 children who were at high risk for type 1 diabetes and followed them for 15 years (2 ). Virtually all the children who had multiple islet autoantibodies developed type 1 diabetes, whereas approximately 15% with a single islet autoantibody progressed to type 1 diabetes. Quantification of islet autoantibodies has proved difficult. Islet cell antibodies were the first autoantibodies identified in type 1 diabetes and are measured on frozen sections of human pancreas by indirect immunofluorescence. The method is technically demanding, labor intensive, difficult to standardize, and currently performed by few laboratories. The other antibodies are most frequently measured by RIA. Recently, nonradioactive ELISA methods have become available commercially for GAD65, IA-2, and ZnT8 (the last was approved in September 2014 by the US Food and Drug Administration for use in the US). Nevertheless, RIA remains the most widely used technique for patient samples and clinical studies. Considerable effort has been undertaken to standardize autoantibody assays. The Centers for Disease Control and Prevention and the Immunology of Diabetes Society established a proficiency testing program, Diabetes Antibody Standardization Program (DASP), in 2000. The goals of DASP are to improve laboratory methods, evaluate laboratory performance, support the development of sensitive and specific measurement technologies, and develop reference methods (http://www. cdc.gov/labstandards/diabetes_dasp.html). The Islet Autoantibody Standardization Program has replaced DASP. Participating laboratories (approximately 50 laboratories in approximately 20 countries) analyze autoantibodies in serum from 50 patients with newly diagnosed type 1 diabetes and 100 controls (3 ). These interlaboratory comparisons have substantially reduced variation among laboratories. Nevertheless, there remains considerable room for improvement. A recent paper in Nature Medicine (4 ) described a sophisticated plasmonic chip for diagnosis of type 1 diabetes via near-infrared fluorescence-enhanced (NIR-FE) detection of islet cell–targeting autoantibodies. The plasmonic chip comprises a 25by 75-mm glass slide that has an irregular surface pattern of tortuous gold islands separated by approximately 10-nm gaps. The gold islands are functionalized with a thiol reagent to introduce carboxyl groups, and these form the attachment points for a layer of a biocompatible branched polyethylene glycol (PEG). The PEG layer is functionalized with Nhydroxysuccinimide groups for attachment of isletspecific antigens (IAA, GAD65, and IA2). These are printed onto the activated PEG surface as an ordered microarray with approximately 400-nm-diameter features. The assay uses 2 L blood obtained from a finger stick. The blood is diluted 1:10 and applied to the array. Bound autoantibody is detected with a fluorescent IRDye800-conjugated antihuman IgG antibody [simultaneous detection of IgG, IgA, and IgM antibodies was achieved with a combination of cyanine 3 (Cy3), IRDye800, and Cy5 labels, respectively]. Bound dye is then detected with a NIR scanner. The entire assay can be 1 Department of LaboratoryMedicine,NIH, Bethesda,MD; 2 Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, Philadelphia, PA. * Address correspondence to this author at: Department of Pathology and LaboratoryMedicine, Hospital of the University of Pennsylvania, 3400 Spruce St, Philadelphia, PA 19104-4283. Fax 215-662-7529; e-mail [email protected]. Received November 12, 2014; accepted December 3, 2014. Previously published online at DOI: 10.1373/clinchem.2014.233346 © 2014 American Association for Clinical Chemistry 3 Nonstandard abbreviations: IAA, insulin autoantibody; GAD65, glutamic acid decarboxylase, 65-kDa isoform; IA-2, insulinoma-associated antigen 2; ZnT8, zinc transporter 8; DASP, Diabetes Antibody Standardization Program; NIR-FE, near-infrared fluorescenceenhanced; PEG, polyethylene glycol; Cy, cyanine. Clinical Chemistry 61:6 794–796 (2015) Perspective