An enzyme detection device or enzyme detection kit for detecting the presence in a test sample of cleavage activity of a sialidase enzyme, the device or kit comprising: (i) an indicator molecule comprising (a) a peptide comprising the following sequence: X 1 -X 2 -X 3 [Gal-Sial]-X 4 -X 5 (SEQ ID NO: 17) wherein: Sial is a sialyl group; X 3 is an amino acid comprising a glycosyl acceptor group and is selected from Ser, Thr, Tyr, Hyl, Hyp, Asn, Arg or phosphoserine, preferably wherein X 3 is Ser; and X 1, X 2, X 4 and X 5 are independently selected from any amino acid provided that at least one, preferably at least two or three, of X 1, X 2, X 4 and X 5 is a D-amino acid and/or a non-standard amino acid or a non-natural amino acid; and (b) a capture site which remains intact following cleavage of the sialyl group from the indicator molecule by a sialidase enzyme present in the sample; (ii) a capture zone to receive the test sample, wherein the capture zone comprises capture molecules capable of binding to the capture site of the indicator molecule, irrespective of whether or not the indicator molecule has been cleaved, in order to immobilise the indicator molecule; and (iii) binding molecules capable of binding to the de-sialylated derivative of the indicator molecule, wherein the binding molecules are incapable of binding to the indicator molecule unless and until cleavage of the sialyl group from the indicator molecule by sialidase enzyme present in the sample has occurred; and wherein the binding molecules are antibodies having a heavy chain with 3 CDRs and a light chain with 3 CDRs, wherein the heavy chain CDR1 has SEQ ID NO:1; the heavy chain CDR2 has SEQ ID NO:2; the heavy chain CDR3 has SEQ ID NO:3; the light chain CDR1 has SEQ ID NO: 4; the light chain CDR2 has SEQ ID NO: 5; and the light chain CDR3 has SEQ ID NO: 6. (i) an indicator molecule comprising (a) a peptide comprising the following sequence: X 1 -X 2 -X 3 [Gal-Sial]-X 4 -X 5 (SEQ ID NO: 17) wherein: Sial is a sialyl group; X 3 is an amino acid comprising a glycosyl acceptor group and is selected from Ser, Thr, Tyr, Hyl, Hyp, Asn, Arg or phosphoserine, preferably wherein X 3 is Ser; and X 1, X 2, X 4 and X 5 are independently selected from any amino acid provided that at least one, preferably at least two or three, of X 1, X 2, X 4 and X 5 is a D-amino acid and/or a non-standard amino acid or a non-natural amino acid; and (b) a capture site which remains intact following cleavage of the sialyl group from the indicator molecule by a sialidase enzyme present in the sample; (a) a peptide comprising the following sequence: X 1 -X 2 -X 3 [Gal-Sial]-X 4 -X 5 (SEQ ID NO: 17) wherein: Sial is a sialyl group; X 3 is an amino acid comprising a glycosyl acceptor group and is selected from Ser, Thr, Tyr, Hyl, Hyp, Asn, Arg or phosphoserine, preferably wherein X 3 is Ser; and X 1, X 2, X 4 and X 5 are independently selected from any amino acid provided that at least one, preferably at least two or three, of X 1, X 2, X 4 and X 5 is a D-amino acid and/or a non-standard amino acid or a non-natural amino acid; and Sial is a sialyl group; X 3 is an amino acid comprising a glycosyl acceptor group and is selected from Ser, Thr, Tyr, Hyl, Hyp, Asn, Arg or phosphoserine, preferably wherein X 3 is Ser; and X 1, X 2, X 4 and X 5 are independently selected from any amino acid provided that at least one, preferably at least two or three, of X 1, X 2, X 4 and X 5 is a D-amino acid and/or a non-standard amino acid or a non-natural amino acid; and (b) a capture site which remains intact following cleavage of the sialyl group from the indicator molecule by a sialidase enzyme present in the sample; (ii) a capture zone to receive the test sample, wherein the capture zone comprises capture molecules capable of binding to the capture site of the indicator molecule, irrespective of whether or not the indicator molecule has been cleaved, in order to immobilise the indicator molecule; and (iii) binding molecules capable of binding to the de-sialylated derivative of the indicator molecule, wherein the binding molecules are incapable of binding to the indicator molecule unless and until cleavage of the sialyl group from the indicator molecule by sialidase enzyme present in the sample has occurred; and wherein the binding molecules are antibodies having a heavy chain with 3 CDRs and a light chain with 3 CDRs, wherein the heavy chain CDR1 has SEQ ID NO:1; the heavy chain CDR2 has SEQ ID NO:2; the heavy chain CDR3 has SEQ ID NO:3; the light chain CDR1 has SEQ ID NO: 4; the light chain CDR2 has SEQ ID NO: 5; and the light chain CDR3 has SEQ ID NO: 6.