A method of assessing a level of secretion of an analyte by a biological cell, or a population of biological cells generated therefrom, the method comprising: introducing the biological cell into a sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) of a microfluidic device, wherein the microfluidic device comprises an enclosure having a flow region, wherein the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) has an isolation region and a connection region fluidically connecting the isolation region to the flow region, wherein the isolation region and the connection region are configured such that components of a fluidic medium in the isolation region are exchanged with components of a fluidic medium in the flow region substantially only by diffusion, wherein the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) is fluidically connected to the flow region, and wherein the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) contains a first fluidic medium; allowing the biological cell, or the population of biological cells generated therefrom, to secrete an analyte comprising an exogenous tag into the first fluidic medium within the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426); introducing a second fluidic medium into the flow region, wherein the second fluidic medium comprises a plurality of reporter molecules, and wherein each reporter molecule comprises: a binding component configured to bind the exogenous tag of the secreted analyte; and a detectable label; allowing a portion of the plurality of reporter molecules to diffuse from the flow region into the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) and bind to the analyte secreted therein, thereby producing a plurality of reporter molecule: secreted analyte (RMSA) complexes, wherein unbound reporter molecules diffuse more rapidly than the plurality of RMSA complexes; and detecting reporter molecules located within an area of interest within the microfluidic device, wherein the area of interest includes at least a portion of the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426). introducing the biological cell into a sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) of a microfluidic device, wherein the microfluidic device comprises an enclosure having a flow region, wherein the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) has an isolation region and a connection region fluidically connecting the isolation region to the flow region, wherein the isolation region and the connection region are configured such that components of a fluidic medium in the isolation region are exchanged with components of a fluidic medium in the flow region substantially only by diffusion, wherein the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) is fluidically connected to the flow region, and wherein the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) contains a first fluidic medium; allowing the biological cell, or the population of biological cells generated therefrom, to secrete an analyte comprising an exogenous tag into the first fluidic medium within the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426); introducing a second fluidic medium into the flow region, wherein the second fluidic medium comprises a plurality of reporter molecules, and wherein each reporter molecule comprises: a binding component configured to bind the exogenous tag of the secreted analyte; and a detectable label; a binding component configured to bind the exogenous tag of the secreted analyte; and a detectable label; allowing a portion of the plurality of reporter molecules to diffuse from the flow region into the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426) and bind to the analyte secreted therein, thereby producing a plurality of reporter molecule: secreted analyte (RMSA) complexes, wherein unbound reporter molecules diffuse more rapidly than the plurality of RMSA complexes; and detecting reporter molecules located within an area of interest within the microfluidic device, wherein the area of interest includes at least a portion of the sequestration pen (424, 426, 428, 524, 526, 528, 624, 924, 1024, 1124, 1126, 1424, or 1426).