Optical coding of mammalian cells using semiconductor quantum dots

ANALYTICAL

BIOCHEMISTRY

Analytical Biochemistry 327 (2004) 200–208

www.elsevier.com/locate/yabio

0003-2697/$ - see front matter  2004 Elsevier Inc. All rights reserved.

doi:10.1016/j.ab.2004.01.031

Optical coding of mammalian cells using semiconductor

quantum dots

Larry C. Mattheakis,¤

Jennifer M. Dias, Yun-Jung Choi, Jing Gong,

Marcel P. Bruchez, Jianquan Liu, and Eugene Wang

Quantum Dot Corp., 26118 Research Road, Hayward, CA 94545, USA

Received 25 September 2003

Abstract

Cell-based assays are widely used to screen compounds and study complex phenotypes. Few methods exist, however, for multiplex￾ing cellular assays or labeling individual cells in a mixed cell population. We developed a generic encoding method for cells that is based

on peptide-mediated delivery of quantum dots (QDs) into live cells. The QDs are nontoxic and photostable and can be imaged using

conventional Xuorescence microscopy or Xow cytometry systems. We created unique Xuorescent codes for a variety of mammalian cell

types and show that our encoding method has the potential to create 1100 codes. We demonstrate that QD cell codes are compatible

with most types of compound screening assays including immunostaining, competition binding, reporter gene, receptor internalization,

and intracellular calcium release. A multiplexed calcium assay for G-protein-coupled receptors using QDs is demonstrated. The ability

to spectrally encode individual cells with unique Xuorescent barcodes should open new opportunities in multiplexed assay development

and greatly facilitate the study of cell/cell interactions and other complex phenotypes in mixed cell populations.

 2004 Elsevier Inc. All rights reserved.

Keywords: Quantum dots; Multiplexed cell-based assays; Spectral encoding; Receptor; Nanocrystal

The growing size of compound libraries and thera￾peutic targets has driven the need for new screening tech￾nologies. The desire to develop new methods for

massively parallel analyses has led to the development of

microarray chips [1–5] and encoded microsphere beads

[6–11] for use as biosensors and for studying nucleic

acids and proteins. These methods have been useful for

studying biochemical interactions, but there has been

limited progress to extend these approaches to cell-based

screening. Cell-based assays are widely used to screen the

activities of compounds against important membrane

receptor targets or to provide important preclinical data

on a compound’s toxicity or bioavailability.

To multiplex cell-based assays, it is possible to use

positional cell arrays, but these systems require sophisti￾cated robotic systems or unique substrate surfaces that

are cell-type speciWc. Cell patterning via surface modiW￾cation of the substrate can be accomplished by chemical,

photochemical, or lithographic methods [12–16]. Micro￾fabrication of nanowells on a membrane surface has also

been used to construct cell microarrays [15]. An alterna￾tive approach, transfected cell microarray, is based on

culturing mammalian cells on glass slides printed with

deWned cDNAs [17]. The cells take up the DNA and

create deWned locations of transfected cells on the slide

surface.

To create a more versatile multiplexing strategy for

cell-based assays, it would be desirable to encode indi￾vidual cells with unique identiWer barcodes. Such a sys￾tem could then be used for a variety of cell types and

would not require that cells adhere to an array surface.

Encoded cells would also be compatible with standard

single cell analysis platforms such as microscopy or a

Xuorescence-activated cell sorter (FACS).1

¤ Corresponding author. Present address: Cytokinetics, Inc., 280

East Grand Ave., South San Francisco, CA 94080, USA; Fax: 1-650-

624-3010.

E-mail address: [email protected] (L.C. Mattheakis).

1 Abbreviations used: FACS, Xuorescence-activated cell sorter; QD,

quantum dot; CHO, Chinese hamster ovary; GPCR, G-protein￾coupled receptor, HA, hemagglutinin; PBS, phosphate-buVered saline.