A method of probing multiple targets in a biological sample comprising: (a) binding at least one probe to one or more targets present in the biological sample including multiple targets; (b) detecting a signal from the at least one probe bound in step (a); (c) contacting the sample comprising the bound probe of step (a) with an electron transfer reagent, wherein said electron transfer reagent is a reagent that can engage in a photoreaction with a molecule capable of undergoing photoexcitation, and an additive which prevents target modification in step (d) below wherein said additive is selected from a free radical scavenger or a quencher for singlet oxygen; (d) irradiating the sample of step (c); (e) binding at least one probe to one or more targets present in the sample of step (d); and (f) detecting a signal from the probe bound in step (e); wherein the electron transfer reagent is a borate salt represented by the following structural formula: wherein: each R 1, R 2, and R 3 is, independently, an alkyl, an alkenyl, an akynyl, an aryl or a heteroaryl, wherein said alkyl, alkenyl, alkynyl, aryl or heteroaryl is optionally substituted with one or more substituents selected from the group consisting of (C 1 -C 4)alkyl, (C 1 -C 4)alkoxy, (C 1 -C 4)alkylamino, amino, hydroxyl, cyano, halogen, or nitro, R 4 is an alkyl, an alkenyl, or an akynyl, wherein said alkyl, alkenyl, or alkynyl is optionally substituted with one or more substituents selected from the group consisting of (C 1 -C 4)alkyl, (C 1 -C 4)alkoxy, (C 1 -C 4)alkylamino, amino, hydroxyl, cyano, halogen, or nitro, and M + is selected from the group consisting of organic and inorganic cations. (a) binding at least one probe to one or more targets present in the biological sample including multiple targets; (b) detecting a signal from the at least one probe bound in step (a); (c) contacting the sample comprising the bound probe of step (a) with an electron transfer reagent, wherein said electron transfer reagent is a reagent that can engage in a photoreaction with a molecule capable of undergoing photoexcitation, and an additive which prevents target modification in step (d) below wherein said additive is selected from a free radical scavenger or a quencher for singlet oxygen; (d) irradiating the sample of step (c); (e) binding at least one probe to one or more targets present in the sample of step (d); and (f) detecting a signal from the probe bound in step (e); wherein the electron transfer reagent is a borate salt represented by the following structural formula: wherein: each R 1, R 2, and R 3 is, independently, an alkyl, an alkenyl, an akynyl, an aryl or a heteroaryl, wherein said alkyl, alkenyl, alkynyl, aryl or heteroaryl is optionally substituted with one or more substituents selected from the group consisting of (C 1 -C 4)alkyl, (C 1 -C 4)alkoxy, (C 1 -C 4)alkylamino, amino, hydroxyl, cyano, halogen, or nitro, R 4 is an alkyl, an alkenyl, or an akynyl, wherein said alkyl, alkenyl, or alkynyl is optionally substituted with one or more substituents selected from the group consisting of (C 1 -C 4)alkyl, (C 1 -C 4)alkoxy, (C 1 -C 4)alkylamino, amino, hydroxyl, cyano, halogen, or nitro, and M + is selected from the group consisting of organic and inorganic cations. each R 1, R 2, and R 3 is, independently, an alkyl, an alkenyl, an akynyl, an aryl or a heteroaryl, wherein said alkyl, alkenyl, alkynyl, aryl or heteroaryl is optionally substituted with one or more substituents selected from the group consisting of (C 1 -C 4)alkyl, (C 1 -C 4)alkoxy, (C 1 -C 4)alkylamino, amino, hydroxyl, cyano, halogen, or nitro, R 4 is an alkyl, an alkenyl, or an akynyl, wherein said alkyl, alkenyl, or alkynyl is optionally substituted with one or more substituents selected from the group consisting of (C 1 -C 4)alkyl, (C 1 -C 4)alkoxy, (C 1 -C 4)alkylamino, amino, hydroxyl, cyano, halogen, or nitro, and M + is selected from the group consisting of organic and inorganic cations.