A biosensor for glucose, comprising a glucose-binding protein and a reporter group that transduces a detectable signal, wherein the glucose-binding protein comprises a mutant of a glucose-binding protein from Thermus scotoductus (tsGBP2; SEQ ID NO: 2, 10, or 110), wherein the reporter group comprises a fluorophore and, wherein the reporter group is attached to the glucose-binding protein so that a signal transduced by the reporter group when the glucose-binding protein is bound to glucose differs from a signal transduced by the reporter group when the glucose-binding protein is not bound to glucose, wherein the glucose-binding protein does not comprise a Ca 2+ binding site, wherein the-glucose-binding protein does not comprise an enzyme; wherein the glucose-binding protein comprises an amino acid sequence that is at least 90% identical to the amino acid sequence of SEQ ID NO: 10 or 110; wherein the reporter group is attached to a cysteine substitution at position W8, or at position W9, or at position D12, or at position E13, or at position G41, or at position H66, or at position H119, or at position W167, or at position W224, or at position W244, or at position K312, or at position H348 of SEQ ID NO: 10 or 110, respectively, in said glucose-binding protein and each position is counted in tsGBP2 with the signal peptide replaced with a methionine (SEQ ID NO: 10 or 110); wherein the glucose-binding protein has no insertions compared to the naturally occurring Thermus scotoductus glucose-binding protein; and wherein the glucose-binding protein comprises (i) less than 5, 4, 3, 2, or 1 deleted amino acids at the C-terminus, and/or (ii) less than 5, 4, 3, 2, or 1 deleted amino acids at the N-terminus compared to the naturally occurring Thermus scotoductus glucose-binding protein. wherein the glucose-binding protein comprises a mutant of a glucose-binding protein from Thermus scotoductus (tsGBP2; SEQ ID NO: 2, 10, or 110), wherein the reporter group comprises a fluorophore and, wherein the reporter group is attached to the glucose-binding protein so that a signal transduced by the reporter group when the glucose-binding protein is bound to glucose differs from a signal transduced by the reporter group when the glucose-binding protein is not bound to glucose, wherein the glucose-binding protein does not comprise a Ca 2+ binding site, wherein the-glucose-binding protein does not comprise an enzyme; wherein the glucose-binding protein comprises an amino acid sequence that is at least 90% identical to the amino acid sequence of SEQ ID NO: 10 or 110; wherein the reporter group is attached to a cysteine substitution at position W8, or at position W9, or at position D12, or at position E13, or at position G41, or at position H66, or at position H119, or at position W167, or at position W224, or at position W244, or at position K312, or at position H348 of SEQ ID NO: 10 or 110, respectively, in said glucose-binding protein and each position is counted in tsGBP2 with the signal peptide replaced with a methionine (SEQ ID NO: 10 or 110); wherein the glucose-binding protein has no insertions compared to the naturally occurring Thermus scotoductus glucose-binding protein; and wherein the glucose-binding protein comprises (i) less than 5, 4, 3, 2, or 1 deleted amino acids at the C-terminus, and/or (ii) less than 5, 4, 3, 2, or 1 deleted amino acids at the N-terminus compared to the naturally occurring Thermus scotoductus glucose-binding protein.